Well, there's a lot in your post...
Our OL at the end of 2018 looked outstanding, but we regressed replacing two starters and looked pretty bad in 2019 at the beginning. Last year I think they improved just like they did in 2018, but why the regression? Pretty easy on the surface to point to 2 starters lost and a center playing that had literally never done it before. But when you dig down deeper, it was more about what we were running as well. Austin was not pleased with the east/west running situation as our line was not built for that, Jaimes, Farniok, Wilson are all north/south guys. When Washington would bounce outside no matter what, and then Martinez would pull and throw despite there being a lane (remember Frost mouthing "run the ball" to him that one game). So between calls to go to the sideline, then when we did have north/south calls us not making that decision, it got away from us a bit.
But to your point, we had zero WRs last year besides JD, line struggled right away, snaps were inconsistent, kicked our most talented RB off the team, and had communication issues with the offensive coordinator getting the play down in a timely manner. We are in a much better spot this year. The thing that will be tough is you have one proven RB, and then Wandale at WR. We have a ton of incoming talent at WR, but we said that before entering 2019. In fact, you can go back and find quotes on twitter and message boards about guys like Houston, Nance, and Chase earning significant playing time. Now, Manning and Betts are even better than our 2019 class, but I always hesitate to get excited based on who we brought in for a recruiting class.
I think your main question was about the OL and i'm extremely optimistic there. The bottom line is we return all 5 starters, so we could go with the same group and get at least a little improvement which would be great based on how they were playing towards the end of the year and with Austin developing the run game plan for 2020. But I think they know our best line is with Farniok at guard, so despite us not starting the same 5, we could be leaps and bounds better.
OL will be good this year. We need to find consistency at WR and our offense could be pretty potent.