yer that is a big difference, but your average as gone up by a few... strange
DLSS go's on a sliding scale, from quality to performance.
Set ever setting in the game to max that will drop your fps, then use DLSS to tune.
it will be set to quality by default because your system is a good spec, just drop it one notch at a time.
can i ask what you paid for the 4080s? because it a lot of money for 13% upgrade over the 3090.
the money for me would be better spent of 14700k or 7800x3d
upgradeing from a 3090 right now is 4090 or pointless, the 3090 is not old enough yet for a 80 card to be a lot better that would be next gen