This is dead on. The "too muscular" for this or that is an old, outdated narrative.
This is either an injury issue or a mechanical issue or a combination of the two.
Another poster referenced hall of fame NFL QBs who are not bulky to support this argument. For a guy with Dungeys somatatype, building mass takes a great deal of time and effort. NFL QBs have to prioritize their time and therefore choose to spend more time on general physical preparedness, film study and throwing mechanics rather than devote it to gaining and maintaining muscle mass.
Also, there are plenty of baseball players that are more muscular than ED and don't have any problems with throwing.