Lots of hyperbole in your post, including the argument that 2018 is CTA's "best chance" at beating Maryland, Minnesota and Purdue. Maryland's coach, Durkin, has proven he can recruit. He's yet to prove he can be a successful head coach. Fleck's first year at Minnesota produced a 5-7 record after the Gophers were 9-4 in 2016. Brohm had a nice first season at Purdue but we'll see whether he can sustain that and/or how long he sticks around in WL.Allen has a lot of competition in the "middle class" of the big ten. Frost went 13-0 at Ucf and beat Auburn in a bowl. Durkin and Fleck are making splashes in recruiting. Brohm is winning and recruiting better. Thank goodness for Lovie Smith stealing from Illinois and Kyle Flood destroying Rutgers.
I still believe 2018 is Allen's year to make or break. It's his best chance at beating Maryland, Purdue and Minnesota and continuing his recruiting momentum. If IU loses to them and misses out on a bowl AGAIN, then he's lost the narrative to those coaches and and the message out there becomes that he's destined for the cellar of the Big Ten. Allen MUST win!!
Except for a couple of teams, it's pretty tough to project too far out in the Big Ten. The jury is still out on all the guys/teams you mentioned and whether - - and for how long - - those games remain winnable games for IU.