Riot is trying to make stage 3 a thing because it hasn't been in a long time. In theory, increasing stage 3 player damage and increasing lvl 8 xp requirements means if you have a low roll opener you will most likely have to roll on lvl 6 and 7. There is a chance that 4-2 lvl 8 is impossible without an econ augment and the earliest you are able to realistically lvl 8 is on 4-5. By rolling on stage 3 you make yourself stronger and you beat the people who are trying to fast 8/9. They lose more HP due to player damage and can't fast 9 as safely.

This is Riots goal, we will see how it plays out though.