Even if you're fine with Barrington and Ryan starting the team currently is one injury to any of them away from having to play Thomas or Bradford on nearly every down.
As noted previously, I'd be OK with Ryan and Barrington, assuming the latter is 100%. That's a big if...season ending foot injuries are often quite troublesome. I haven't seen specifics on that injury, but if it's a Lisfranc or even a turf toe, that could spell real trouble. And this also assumes Ryan will continue his progression, about which I am optimistic.
But with no guarantees with respect to those two starters, and the current guys behind them needing upgrades, 2 ILBs are needed as you say. If Barrington can't play, make it 3 ILBs.