Writer Carlos Cisco has indicated that they conceptualized the Breen's solid form as an adaptation that they developed over time, which would track with your idea.
And "The Chase" certainly left some wiggle room for there to be species that were untouched by the Progenitors:
Our scientists seeded the primordial oceans of many worlds, where life was in its infancy. The seed codes directed your evolution toward a physical form resembling ours. This body you see before you, which is, of course, shaped as yours is shaped, for you are the end result.
I agree. We know that there are non-bipedal sapients (eg Tinman, Tholians, some Xindi, Belugas, etc) so there must be some species not made in the image of the Progenitors.
Writer Carlos Cisco has indicated that they conceptualized the Breen’s solid form as an adaptation that they developed over time
Interesting.
It's completely unrelated to the current Disco story arc, but that does make me wonder if the Vorta and other Dominion species would have been aware of the Breen's goo form. The Changelings evolved the ability to shapeshift over time, but were originally solids. having the Breen start out as the soundtrack producers for the "Spider-Man & Venom: Maximum Carnage" video game, and later develop a solid form might seem anathema to the Founders and their worshipers.