If the rQB can't throw he'll be stopped because DC will have 11 in box focused on run - and screens are easy to defend. And if he only token throws that's easily covered as well.
If you have the O-Alignments as you mentioned (just SBB and Big I) think running against a 4-4 Big (Big I) or a 4-4. If the blocking TEs never catch a ball don't have to cover them - or at least not with anydot designed to cover, a strength based LB that "covers man" and then either blitzes/ plays zone accordingly will suffice. If your rTEs can't block then don't have to have power LBs on them, can have the Int/ Coverage LBs over them but doing the same. And those strength dots will cause fumbles once you get a couple of monster hits on you and morale starts to hit the 70s.
What you have to account for is that on average, a good run, gets you 2.5-3 yards, a bad one gets you -0.5 - 1.5 and a great one might go for 4 yards (on inside runs). Edge runs are either 40+ yards or -5.

You're probably getting a 10/40/50 split on great/ good/ bad runs if build are equal. Math says you aren't getting 1st downs without passing and if you always run short routes those are getting stopped, if your targets are always the TEs those are just double covered and your strength-based WRs and non-catch HB/ FB draws little to no attention.
A run-focused team (75/25) can win, can control the clock and can grind a defense down but you're still going to have games where passing is how you win. As long as you can do that effectively when the defense you're up against calls for it the approach can work - but just running head-first into a D waiting for you, expect lots of 3 and outs.