I'm a big believer in Williams, and think that the underlying problem is moreso who will fill out the top of the rotation. Taillon and Musgrove are the best two bets on the team, but neither of them are huge strikeout or innings guys as of yet. I think you could say the same about Keller, who won't really register as relevant for another year anyways.
The other way to address starting pitching is by having a phenomenal bullpen. Obviously, Glasnow has had ups and downs, but if he could become a guy who gets used in a multi-innings high leverage role a couple times a week, then the lack of truly dominant front line starters is less of an issue.
Moreover, I'm always a little bit hesitant to talk too heavily in the language of 1,2,3,4,5 starter, etc., because these are abstract categories whose value usually seems to be about complaining how X pitcher isn't a #2 starter, etc. I know that they are useful shorthands, but I'm more talking about what these ideas mean relative to the entire league. There aren't 30 #1 guys, 30 #2 guys, etc.
What we could really use is consistency. Outside of Williams, I don't think the pitching has been a huge problem lately. The bullpen a couple of times, definitely, but in the recent slide, it's been a number of other issues too. If we get a return to consistency from the pitching, i.e., if a bunch of those guys pitch like "3s and 4s," then I think soon enough, we'll rattle off a couple 6-4 or 7-3 stretches. That will be just enough to stay barely relevant, but because the slide has continued (and could still be continuing) for so long, it won't do. We need a real hot streak, and unless some hitters get white hot, the only way that that kind of thing is likely is if we get a really incredible run from some pitchers.
Separate from this, I wonder what would happen if Nova is able to put up a really strong run of games. He won't have huge trade value, but could compete somewhat with a guy like Happ, i.e., a veteran who would give a contender some decent reliability for innings going down the stretch. With Kingham in AAA, Keller eventually knocking on the door, and Glasnow still in the bullpen, moving him even for a marginal return makes a lot of sense.