Riding and ground work harmonize together to help a horse learn all that he can and be as soft and responsive that he can be.
One without the other leaves HUGE holes in training.
Imagine a horse that knew groundwork so well and you got on and he wasn't used to carrying you around. He'd be very unbalanced and it would be hard for him to carry out what he knows.
Imagine a horse that's great under saddle but doesn't understand that those cues you taught him up there make sense on the ground as well.
Together, the horse has no confusion or hesitation on what to do as long as you are clear in your cues. :)
I didn't read through all of the articles but I did pull ones that I thought would be interesting to look through. Everyone has a different view on the same thing. Flexion to some means carrot exercises and not that little change of angle in the poll bones (which I have yet to memorize lol!) etc. etc.
The BEST thing you can do, is get educated as much as you can. Then you can pick and choose what works best for your horse, and yourself.