It does not remove end lag. It allows you to take advantage of the buffer windows to maximize whatever frames of advantage you have to work with when it comes to using air drift for combos and set-ups. It does not give you more to work with so much as let's characters more easily access what is already there, but could not consistently use due to human limitations.
You know how in anime you have that elder that unlocks a character's "true power"? That's Slingshot. Just maximizing what already exists.
Kazuya does benefit. People are already coming up with new combos and shield break set-ups. Jumping to conclusions on day 1? Nah. Just mess with the tech and be a student of the game. Let the game show you a conclusion. Don't be in a rush to reach one. Besides Kazuya's meta still has way more juice even if this did not help him. Kaz players aren't even doing CDC to break past zoning yet.
As far as Terry compared to shoto's, I would love to know why you think their ceiling is higher when Terry has access to better burst options which demands respect and sets the pace for him to Power Wave. That alone makes him more complex with a higher ceiling than Ken who essentially must play around his opponents and cannot make his opponent do anything. Ken as a character cannot enforce his will. He relies heavily on vortex type mix-ups that let him create scramble situations which can snowball out of control for his opponent if they do not choose the correct defensive option. I think perhaps you are so used to seeing Riddles play a certain way that you may think Terry has a low ceiling comparatively when he doesn't. His set-play is arguably the best of the FGC chars, especially his ability to trap landings. Riddles simply does not do it. He relies heavily on "Abare" i.e converting stray hits into combos for damage and kills.
Ryu is also fairly one dimensional, but he is quite good at what he does and can sit on a lead with the greatest of ease. His set-play is easier to see and abuse compared to Ken as well. Uair knocks you up. Tatsu knocks you up. So do an ender that knocks the opponent up and throw a hadouken as they fall so they have something to deal with. Apply pressure to their landing. Terry has VERY similar traps, but with even more options thanks to Burn Knuckle and Crackshoot. Riddles just refuses to try to trap landings. He won't even try it with Kazuya even though EWGF is THE anti-air of the gods. Why he doesn't do it much, I cannot say. Might just be his mindset to focus hardcore on conversions. I presume this is why his Kazuya is superior to his Terry. Kazuya gets much more out of stray neutral wins compared to literally every other character in the game.
However, when we look at shoto players they DO engage in set-play, landing traps, and tech traps. So if the strongest Terry is not doing those things, but the strongest shoto's are and the results are comparable between them; doesn't it follow that if the strongest Terry DID start utilizing those aspects of his game that the gap in results would widen?
Please share your thoughts.