Love your wording in your questions, steers me away from nagging lol.
I'll try to be concise.
First we can all agree production follows progression and not the other way around, right? This is the fundamental flaw of XP.
The problem with practice drills and dev traits are they are too binary. I bet the Raiders coaches tried their *** off on focusing on Jamarcus in practice but he didn't "gain any XP" anyway. The problem in Madden is you know OK I click this button for 1500 XP for this guy or 3000 XP for this guy. No challenge or complexity.
I feel like the point of franchise is to 1) have your games string together and mean something and 2) build a team. Team building with XP and dev traits is just not challenging or complex at all.
I appreciate the step they took to bandaid the issue and I think people who can stomach XP will really enjoy it, but it's not enough for me.
Weighted potentials modeling progression from real life data would be probably an effective and easier way to go about things, and then allow the user to effect these percentages by hiring certain coaches with different specialties and holding camp and blah blah blah I've already laid that part out in my post.
But I fear the longer we build on XP as the base we are just wasting time or getting to the point of no return.