You don't even actually "Choose ones for your deck" you just have them and choose upon Venturing while not in a dungeon. Much like how tokens aren't stored anywhere and you just make them upon prompting. I believe.
That bit only applied to contraptions, but I'd say that there are some similar overarching design concerns. THe power level of any future venture cards is tied to the existing dungeons, unless they make new dungeons, in which case that changes the power level of the old venture cards.
I like the mechanic but the execution is wonky on the meta level. What happens when they want to make more dungeons? Reminds me of Contraptions, where some are just better than others, but you can choose whichever you want in your deck without any drawback. Don't take up sideboard space? Really?
Is Phandelver really that iconic? I guess they're stuck with just Forgotten Realms locations though. Which was a mistake to begin with.
Phandelver is the default entry point for new players in 5E, so I'd call it iconic. I've been in multiple Phandelver campaigns, and it was featured on the podcast The Adventure Zone. It's very popular for new DM's in particular.
I'm not really up on the newer adventure modules/ source books.
Is Phandelver fondly remembered? I've mostly heard negative things, so I would have preferred a card based on a tested classic.