I'll split the difference on the "scout the helmet" thing. Each player is their own man, and one guy's failure doesn't affect the next. At the same time, coaches tend to recruit similar kinds of athletes for their schemes, and coach them up in similar ways. I'm not a Michigan fan, so I don't know if they are still running Harbaugh's defensive system or not.
What I will say is that Mazi was a really terrible draft prospect - measurables that didn't match the hype, and the worst volume-stat production of any 1st round DT this century. He looks like a plain overdraft.
Taco surprised me at how hard he busted. He was a 2 year starter with good volume stats, decent sabermetrics (15% pass rush win rate, looking it up), and pretty decent measurables outside of being extremely slow (4.92 40). 1st round was an overdraft, cause he just didn't have that kind of juice, but he seemed like he at least had an NFL-roster floor. If Taco was coming out into the draft today, I'd rate him as a late 2nd or 3rd rounder for like a Tyrone Crawford DE/DT tweener role.
Anyway, I think Dallas pretty clearly mis-evaluated both of those guys, and it's not even hindsight. I don't think it's a Michigan problem, those are just Dallas problems.
Kenneth Grant and Graham both have 2 years of good tape on a great defense, and on a not so great one. Graham is just a stud, and he's going to be good no matter what. Grant looks like a load at 1T, but if we mis-evaluate him and draft him top 10, he'll be another "Michigan bust", cause he's just not that caliber of player.