Dont try and mix rules and flavor, it always ends badly.

That can be addressed on two levels: mechanics and flavor.

In terms of mechanics, it's simple: players are in no sense planeswalkers and planeswalkers are in no sense players. The only overlap is that both can be attacked and both can be dealt damage (the latter of which they also share with creatures). Planeswalkers are just permanents with a restriction on when their abilities can be activated and the capability of being removed via attacks and other damage.

The reason burn can hit planeswalkers is that they wanted to players to have that option of dealing with them. The reason it's a blanket "all player-directed burn also works on planeswalkers", implemented via the redirection rule or the upcoming errata, is that planeswalkers were introduced so late in the game and they needed a way to grandfather in all the burn that was printed before planeswalkers existed. If planeswalkers had been there from the start, we'd probably have burn cards hitting any of the seven combinations of players, planeswalkers, and creatures.

It's normal for permanents to be dealt damage. Creatures have done that since the game began. And there's no lie when it happens. If you use Chandra's Defeat on a planeswalker, the Defeat deals damage to the planeswalker, and the planeswalker has then been dealt damage by the Defeat. On the other hand, if you somehow used Bump in the Night on a planeswalker, it would be a lie: the Bump says to cause its target to lose life, but the planeswalker doesn't lose life, and then hasn't lost life.

In order for that to work at all, it would either require a rule that makes cards do something unrelated to what they say they do, or utterly bizarre errata ("Choose target opponent or planeswalker. If the target is a player, he or she loses 3 life. If the target is a planeswalker, remove three loyalty counters from it.")

In terms of flavor, sure it's weird, but so is everything else. Again, the only similarity between players and the planeswalker game objects is that they can both be attacked and dealt damage. If you think that, because they conceptually represent the same thing and should thus work the same way, you need to explain why they don't. Why can planeswalkers repeatedly use the same "spells" when planeswalkers are limited by what they have in their hand and what mana they can produce? Why are planeswalkers immune to discard and milling? Why can't players be hit by Dreadbore?

And, of course, there's the issue of why creatures are treated so differently from both players and planeswalkers, and of why cards even have the targeting restrictions they do. Why are creatures immune to being spiked (or axed) by lava? Why can't creatures be bumped in the night? There's no flavor explanation for these things. They just designed different cards to affect different things.

Because the flavor is so fluid and so full of weirdness and exceptions, flavor consistency can't be used to justify any particular change.

Thinking about it, my choice for how to deal with this would be just from now on print most burn spells with "target creature, planeswalker or player" and leave past spells unchanged.

One reason would be to prevent all the ugly errata that is going to come from this, and all the problems that come from that. That would in all likelihood make plenty of past burn spells much harder to reprint in conventional sets, but nothing is stopping them from reprinting them in extra sets anyway, which can handle this kind of discrepancy/outdated mechanics. Not to mention that either the errata is going to be inconsistent or spells like Earthquake are going to be really ugly, which is going to make them hard to reprint anyway.

Another would be because that could increase variety in the burn spells used in competitive play. Right now, Bolt is the single best burn spell -- but what if Lightning Strike + planeswalkers entered the mix? Wouldn't it be interesting if Bolt, being unable to hit planeswalkers, was competing with a less efficient option that could do so? That might just increase a lot of design space for burn spells, since there are now three possible targets to hit.

Plameswalkers are too powerful and hard to balance, they should errata all walkers to not exist.

So you would nerf Lightning Bolt? Interesting.

I think they will issue a blanket errata, that burn that targets players can target planeswalkers, and that the other spells, like Blightning or Earthquake, will not be able to damage planeswalkers. This opens up a bit of the design space that you were thinking of, without having too big an impact on eternal formats. Which I don't play, so maybe I'm wrong?

It's an ugly change, but even ugly bullets need biting. I'd say that the change is less ugly than the redirection rules we have now.

I'm on board with Rio. Get rid of the redirection rule, print new burn that cares about planeswalkers, and leave past burn spells be. This doesn't feel like a case where the errata will be worth the headache. You'd make planeswalkers in older formats better for a while, sure. So, Jace TMS, Dak and Liliana. Three cards. Hell, you might incentivize players to add more PWs. Planeswalkers are only dominant in Standard; stop worrying about the past and just move forward.

That wouldn't just affect the past, though. It would render hundreds of cards unsuitable for reprinting in Standard-legal expansions. That includes a lot of famous/popular cards and a lot with very good names.

Sure, but only if we treat players and planeswalkers as exactly similar entities, which we'll never do practically. You can still reprint Lightning Bolt; it just won't be able to take out whatever incarnation of Jace is currently in Standard. Someone pointed out earlier that life loss is something that you'd thematically want to change to affect planeswalkers but that mechanically takes too much rules-twisting to do. I think you just take the same line with damage. I don't think that finite language is a good enough barrier to a policy like this. Reprints are fairly few as is, and this affects only a small subset of cards. This sort of errata just seems like it will be too inconsistent to have a positive effect on the game. There are just too many direct damage cards with too many permutations and riders for any sort of sweeping errata to be easily identifiable.

But would it? Not all burn is "creature or player" burn, and it doesn't seem at all weird that all burn after this would (or should) be "creature, player or planeswalker burn". And it might even diversify decks's burn suite with "3 damage to target creature or player" sharing the spot with "3 damage to target creature or planeswalker", similar to the splits players have to make with Negate/Essence Scatter or other counterspells, depending on the matchup. Doing away with the redirection rule, without errata, basically opens up a large amount of design space, and the obvious designs (Lightning Strike that can hit planeswalkers, for example) can be done right at the introduction of the change.

Dont errata old burn + ban 3 mana lili and jace the wallet sculptor in all formats. Thats the best solution. Then maybe people could play less good walkers.

Way things are going in modern, if there is no errata, looks like only Karn, Ugin and Saheeli Rai are going to be the only viable walkers... And people are going to be ptfo about the new twin!

Edit: Fixed... Forgot to mention why those would be the only ones.

We are gonna end up with a "Bolt target creature or PW" and a "bolt target PW or creature" and a "bolt target PW or Player." Then we will get 3-5 mana cards that have "Bolt X + Y" too.

Mark my words. They won't let the game go far without a cheap way to attack PWs

Maybe not bolt a player + pw. That gives burn in modern and eternal more power.

This will honestly be a bigger errata change then the grand creature type update.

I second this, but I've been saying that for a decade now.

They don't want life loss spells to hit planeswalkers because they want to make red and black spells different from each other. Also black doesn't need it since it can destroy them directly.