The recoil in an AR is generated when the round goes off and during the time that the bolt is locked ....... which remains locked until after the projectile reaches the gas port.
The buffer/spring simply responds to reduce the inertia of the bolt moving to the rear 'after' the projectile has passed the gas port (which is properly sized to efficiently move the BCG rewards to unlock the bolt, clear the magazine and cock the hammer) and then provide the force to move the BCG forward again, strip off another round and relock the bolt.
More dampening provided by a heavier buffer, hydraulic buffer, and/or different spring strength combo's (and consequently changes in cycling) may result in a perception of reduced recoil and an actual reduction in muzzle lift, but it's really just the result of the action cycle timing and cushioning of the bolt itself's reaching the end of it's rearward momentum, anf then again when the bolt slams home again, and not actual recoil reduction.
It could stand to reason that this perception of buffer/spring induced recoil reduction (which once again .... is really just bolt cycling damping) should be more pronounced/noticeable in smaller caliber-lighter load combinations, and be more masked in larger caliber and heavier rounds.
I.e. .223 50 grain may resolve changes to the buffer system as more/less recoil, where it would be totally hidden in a 50 cal Beowulf.
But ..... the buffer and spring 'do not' and 'can not' impact recoil 'BECAUSE' ....... the bolt is locked during the time that the recoil is generated, and remains locked until the gas travels back to the piston/bolt and forces the bolt carrier to the rear, unlocking the bolt which then also travels rearward..... and only then does the buffer system come into play.
This is why when you have a valved gas port (like on single shot bench gun, or a piston and/or suppressed ARs) and you turn off the gas port (so the bolt remains locked/no cycling) ........ the recoil remains the same, sans the minor reduction of the BCG inertia that might be felt.
Different weight buffers and BCGs, as well as different strength springs are used to dampen the movement of, and optimize ..... BCG cycling with different loads in different gas system designs, with different BCG weights, and/or modified/supressed gas systems, etc. and can help reduce BCG movement induced muzzle lift ........ but they do not control recoil.
If you're looking to reduce recoil ........ and/or muzzle lift for that mater ..... and not able/wiling to go to a different length gas system (barrel) look into a brake that will accomplish what you want .... for the load you shoot.
You can help to control muzzle lift by tuning the the buffer system and/or BCG weight and using a tunable gas block.
You can also just add weight if that's OK with you and what you use your AR for.