https://en.wikipedia.org/wiki/The_Thing_(1982_film)
one
- Founders - Change shape
- Thing - Change shape
two
- Founders - live in a giant soup and can split off from the soup at will
- Thing - Can divide up the shape at any time into autonomous functional groups
three
- Founders - Fly in space ships
- Thing - Flies in massive space ship
four
- Thing - Doesn’t like fire
- Founders - who likes fire?
I posit that the founders are the Thing, but perhaps a group of founders operating in special operations mode. Or they could be children out on founder Rumspringa like Odo was.
In Chimera (which takes place after Accession) they bumped into a changeling flying alongside their runabout in a form that was space-faring. I guess the argument would be if there exists a creature encountered by a Founder that can travel at (high) warp via some kind of biological or entirely different means than subspace manipulation.