I expect you'd need to ride an identical scoot with a Li150 gearbox to be able to compare the performance difference betwween the 2x gear ratios........... otherwise the Li125 gearbox would just seem normal I guess.
There is no denying the facts the sprocket teeth and ratios show the large gaps.
This 'jump' probably wouldn't be a problem to a rider that is happy to pootle around town and doesn't accelerate hard at every single opportunity .
For someone looking for significant performance upgrade who has gone to the cost and trouble to fit an expensive 200cc upgrade engine it would be bonkers imo to leave an early S3 Li125 gearset in place because the ratios would negate any engine performance increase gained.