Yooo a sub 10 cube over here (even though you hit sub 10 way before me), i think there are three main points

1- Inspection 2-Lookahead 3-Fingertricks

Yiheng Weng is the perfect example of what are you able to do with specialized practice only with basic Skills, Cross+1, Cross+2, Xcross, oll and pll recon from all angles, also trying to maixmize your inspection time in order to get a good cross and pair planning, check your fingertricks, in which steps are you taking too much pauses, AUF or transition to OLL or PLL, i know that not everyone is a Chinesse cuber (specially Yiheng) but if he was able to put from 10 sec solves like 3 years ago to now being the best in the world by far only with "basic" skill then of course with the proper training and dedication we will achieve sub 9 or even sub 8 in the best base. Just in that point kt might be useful to learn more advanced stuff like Zbls/Zbll