I agree with this by and large. Whenever you have an entire unit not doing well, you have to look at scheme, coaching or both.
That said, I think it’s clear that Grob’s problems go beyond the struggles of the other linemen. Consistently leads the league in penalties. And more of those than Smith or Barron ever did. He still misses assignments and sometimes inexplicably blocks no one. Has allowed strip sacks at critical moments that directly affected the outcome of the game. In fact, it seems that most of his screw ups come at very critical moments.
He’s also been at this for 2.5 years. That’s about the time when teams often give up on someone. A lot of the other linemen are in their 2nd seasons.
Adding Thomas solidifies the most important OL position. You get great pass protection, no inopportune penalties (fair or not), and likely one huge step in fixing the running game. At the very least, they would be assured they can run Gurley to the left side now.