I do agree with you, that we don't have a clear-cut, bona fide #1 RB who has seized the reins.
If Jafar Armstrong can look like he did early on in 2018, before all of those injuries, then I'd say that we're in a pretty good situation, but given his history of injuries, I'm not too keen on relying on his being healthy and sound for the whole year.
C'bo Flemister looks like he could be a pretty good power back, if he packed on another 20 pounds of muscle. I don't know what effect the S&C will have during this off-season, though, since there;s only so much that Matt Balis can do remotely.
I don't know what to make of Kyren Williams. All we saw from him last year were a few carries in a couple of games, before getting shut down to preserve the redshirt year. Given his skill set, if Brian Kelly can't find a way for him to play, then there's something wrong. He's got a really good eye for the passing game, both in terms of pass route running and catching the ball, since he used to be a WR in high school.