I think you're not split stepping correctly. As your opponent contacts the ball, you should be in the air at the peak of your split step, such that by the time you land, you know which direction to push off. But since you've already set a playing pattern (fh-bh-fh...) you're always on the move to the anticipated direction. There are a few split steps but they are almost all biased towards the anticipated direction. At 1:00, that split step was more a jump towards the forehand you know you'll be getting. The best split step IMHO is the one at 0:17 because it's more "neutral" than the rest but it's still biased towards the bh. It may work for this drill but in real matches you'll easily be wrong footed.
Personally, if there is one aspect I want to improve on, I'll do a real drill (i.e. having someone feed me balls and doing the same thing repetitively) instead of practising with rallies as you did. So if I want to practice hitting on the run for my forehand, I'll stand on the ad side and have my partner feed a ball to the corner on the deuce side. After hitting, move back to the ad side and repeat. It's not as fun as rally practise but I find it more productive since I can focus on honing one aspect at a time and keep the momentum going rather than distracting myself with too many changing variables, such as poor returns from partner, changing grips from fh to bh etc. Once I've gotten the hang of things, I'll mix them up (e.g. one fh and one bh) but still with fed balls to limit the variables. Then maybe get your partner to feed you balls randomly to your fh and bh. Always split step as if you don't know where the ball will be coming to next. I know it's challenging to convince someone to do drills with fed balls with you. It would be good to find a partner who has something he wants to work on and you guys can take turns to feed balls to each other