In general, RBs are the least important part of the run game equation.
The most important part is having a competent scheme and playcaller. You could have a 2 TE front with the seven studliest blockers in the league, but if the defense has loaded an 8 man box and the linebackers are just staring down the run, you aren't going to get anywhere.
Then, you need to have blockers with enough talent to move the guys in front of them. Just based on past track record, I think the Cowboys have the horses to do this. They haven't been getting push, but I blame the scheme like above.
Then, if the scheme is setting up favorable situations, and the OL is opening holes, then the RB is the problem if he's not seeing the holes or breaking tackles.
Pollard hasn't been as explosive as in the past, but he's not missing holes like Trent Richardson or just laboring through them like 2022 Zeke. I don't think he's the problem, and likewise, switching to Dowdle won't fix anything.