I kinda agree on cutting Sorin. Most expensive walker, worst +1 and the -X is not as needed anymore with the better answers to walkers.
Meh, Sorin is still a strong planeswalker. His +1 has potential to drain our opponents and his -X can allow us to gain life, which is relevant agaisnt aggro and ramp.
Personally I prefer Sorin over Jace.
Jace does a damn good job of filtering for us, but that is about all he does. His -2 gains more value now that we can run more cheap counterspells, but it still likely isn't hugely relevant. His ult doesn't do a great job of closing out games for us either.
Sorin may not filter nearly as well for us, but he still does the job decently while also providing direct damage to the face, more effective removal (read not bounce) that hits both creatures and PWs and gives us some more life gain, and his Ult can actually put someone on a clock, which Jace's doesn't.
While Sorin's -X doesn't seem as necessary anymore with Anguished Unmaking, Cast Out, and Never//Return all available to us, having Sorin around to answer PWs could mean being able to save those other more wide-reaching removal spells (like Cast Out and UA) for other non-creature/non-PW permanents that tend to be a thorn in our side (Tutelage, Visions, Dynavolt, etc). *shrug*
I don't think having that redundancy on PW removal is a bad thing, because all of them have functions outside of just being PW removal. Sorin does a lot more than just function as PW removal, same with Cast Out and UA. Never//Return is a little more narrow, but could still function as GY hate or a chump blocker in a pinch.