…but love the unforeseen consequences.
Guts really do make the bilaterian. Everything follows from making a tube-shaped body plan — all the increased potential for signaling between different tissues multiplies the number of possible developmental histories, and leads to all kinds of novelties. Like a central nervous system. You wouldn’t be reading this if there’d been no gastrulation. Brains, a coelom, a circulatory system, etc. were all side-effects of a successful feeding strategy and triploblasty. You should be grateful to your guts for making you.
Although, if they hadn’t, I suppose the life of a jellyfish isn’t all that bad.