There is no solution to your request. "Instant" and "After" are emulations of an old, poorly designed system and should not even be options. "Gradual" is the only sensible choice, but even this is different between games - it can be "procedurally gradual" by FOV change per frame (so sens adjustment follows a sigmoid curve) or sometimes it's just "gradual over time" (linear sens adjustment).
Even if you attempted a hacky fix, like scaling DPI by zoom transition time using a filter driver or script (which might trigger anti-cheats), you couldn't stop the game from doing its own scaling. This scaling is nearly impossible to reverse engineer unless you have access to the source code, which would still be an extremely inelegant solution.
I'm afraid this just falls under "learn to play the new game," similar to adapting to changes in movement speed, camera pivot point, crosshair position, recoil/sway, and other factors that make targeting feel different in each game.