Lewa still makes much more sense than Mane. Barca already has a bunch of left sided forwards who play a similar position to Mane but no pure strikers like Lewa. The way Barca plays won't suit Mane too good either so I would expect a clear drop off from his Liverpool performances.
Mane is a few years younger but I think Lewa will have much better longevity so they might have a similar amount left in the tank.
Mane had been having a huge dip in form the last 1.5-2 years playing as LW, he was not what he used to be in '16-'20
After being moved to CF to accommodate Diaz at LW, he had re-invented himself...
I don't want him here for LW, but for CF. He has still great finishing in him, he is in much better physical state than Lewa in terms of running and pressing.
Lewa can be better against very deep parked buses (but only slightly) than Mane
but against top opposition in CL where all the above elements are needed Mane is much better