I think there should be some system where you cant max out all stats and instead have a limited amount of stat upgrades you can use (about 2/3 of the way to maxing everything out)
or the max amount of upgrades you can get from a fountain is capped on an overall player experience level which is based on training and overall juice earned
another option is that each of the new base stats being added are trained while the old ones are still bought at fountains, but the effect of these upgrades is now affected by the new base stat levels
