i have been playing guitar for about 4 years. my legato technique is pretty good but it feels sloppy. while using this video to learn and perfect it i realized that my left thumb posture on the neck was incorrect and while fretting the lower strings i would turn my left hand outward. now that i have corrected the posture and technique i feel much slower. should i continue to play with the incorrect technique or keep practicing with the fixed technique even though its slower?

Link to lesson:
https://www.guitarmasterclass.net/solo-guit...o-etude-lesson/