it would be better to make them different than the 18 yo drafted one season before
That makes sense. I would prefer it this way too.
i still believe that we should just have a bigger % of top 19 yo, 70-80 TSP)
This is the desired effect, yeah. 9.49 instead of 8.99 would achieve just that and it would make players look better visually without too much effective improvement. See this way displayed TSP will increase by 4-6 points on avg but real TSP would only increase by 2-3 pts (for the 60+ TSP guys that is).