Exactly. He has been repeatedly beaten on set pieces and his form was already declining before Miles Robinson went down. Zimmerman has only been locked in as a starter since Robinson went down and Richards couldn't get healthy. At the end of WCQ, the question was whether Richards could get enough PT to hopefully supplant Zimmerman. In an ideal world, our starting CBs would be Robinson and Richards with Ream and Zimmerman as capable backups. I think Zimmerman would have been fine as the complimentary CB but he is now being asked to act as lead dog in a World Cup with a looming disaster next to him.
All that said, Long (and the system that Greggg believes his selection supports) is THE issue. All of Greggg's flaws are somehow perfectly exemplified by his selection of this one player. Overreliance on MLS players, continuing to play a high line without fast CBs, selecting favorites, and an inability to adjust to opponents and changing circumstances.
The option to start a capable and experienced EPL CB next to his EPL LB teammate is an unbelievably fortunate opportunity after your starting LCB goes down. The ability to protect your new CB pairing with a double pivot including an in-form EPL 6 in Adams (who so obviously plays better in a double pivot) and a fit-for-purpose Musah is an obvious solution to our defensive dilemma. Just ditch the high line, protect the CBs and play a LCB who has unparalleled chemistry with the LB. OR start two out of form and slow CBs and rigidly adhere to a defensive system (high line) and formation (single 6) that doesn't cater to the strengths of your players. When Aaron Long runs out there against Wales, Greggg's legacy as the worst coach in the history of US soccer will be written.