This issue made me go out and pay $44 for a 5000 yen JPN PSN card and buy the game digitally. I didn't really know what you and others meant by 'knockback'. I thought you were talking about getting hit by the lasers in your 'ship' mode. But now, I think you mean being hit by the lasers in 'Nenshin' (or 'Spirit') mode. In the X360/PCB versions, when you get hit by lasers OR bullets in Nenshin mode and you don't push forward, you get 'nudged' backwards a little bit. In the PS4 version, you get nudged back by the bullets when in Nenshin mode, but not by the lasers. So you are right, this is an issue that needs to be fixed. However, I consider it to be very minor, as you are invincible when in Nenshin anyway (when not holding laser), and I honestly never even noticed this minor thing before.
After playing the PS4 port, I can offer the following comments:
1) Input lag is the same or better than the X360 version (so, 3 or 4 frames). Very responsive. (Note: I am playing the PS4 version on a PS5)
2) The menus look more pixelated on the PS4 version than the X360.
3) The slowdown accuracy on the PS4 version is SO MUCH better than the X360 version (it is way better than the EXA port too). Playing them back to back, the X360 port feels like it runs on fast-forward. This is very close to the PCB, and if they fix that laser 'nudge-back' thing, it will be golden.