Pass blocking depends greatly on movement by the o-line, just getting in the way of the defenders is often enough to give Dak the normal amount of time needed to go through his progressions and read the defense. But run blocking requires pushing on the defenders, coordination with the other members on the line, etc. Pushing requires a lot of strength, something apparently Williams is lacking (still), Martin has back issues, that is probably hurting him. Frederick is not his old self, close which is still better than most centers in the NFL, but his main value is in making line calls which of course has nothing to do with his body.
But IF the line can get back to their old selves, Zeke has the ability to use that and be one of, if not the, top back in the league. Sure others could probably do what Zeke is doing now, but that's their ceiling. Zeke can elevate the running game to a higher level. That's what he's paid for at this point, not so much has game performance.
But note that he's still 8th in the league in yards, 6th in touchdowns, and among the leaders in first down runs. Not too shabby. It's not like he's a poor running back, we've seen what happens when Pollard is run up the middle, seldom gets even a couple of yards, Zeke nearly always gets at least a couple.
As with Dak, Zeke isn't the reason this team is "only" 6-4, it's more than a couple of things, other than coaching, which I think we all agree is mediocre most games.
Look at the Chargers - last year they were 12-4, this year at best they can be 9-7. Last year they got the breaks and made the plays needed to win 12 games, this year not, though they still have Rivers, Gordon, Henry, Bosa, etc. It's a fine line between 6-4 and 8-2, after the season is over we can evaluate this team....