The problem is most people don't know how far from their "perfect form" ceiling they are. You won't know unless you've been there before or you have someone else tell you.
Keystone issue is glute activation. That is the granddaddy.
Id say quadraped glute activation is the best starting point.
If you have a glute activation problem and you don't fix it you will not be able to fix anything else you are having issues with. And if you only fix it a little bit, you will only improve on everything else a little bit.
The goal of the exercise in the vid is to focus on hip movement and keep the back completely still. Much harder than you might think.
Exercises such as these are done so wrong so often that if anyone told me they did glute activation exercises I would basically guarantee they are doing them wrong.
The only person I've ever seen teach a glute activation exercise properly in person was Mike Boyle when he was my professor back in 2004. I've been training in several gyms in two states since.
After that work on kneeling hip flexor mobs and t spine mobs etc... also some adductor dynamic stretches. You can do all of this stuff at the same time. But none of it will come around until the glute activation does.