To me, this statement implies that you either don't understand what a modular synthesizer system is or you haven't kept up with the times. I mean, you literally build your own system by choosing your own components and patching them together however you want. You're free at any time to pull the patch cables and start over. Add one new module changes the entire system.
Other than the fact that you need to be able to plug it into something, I can't imagine anything being much further from the definitions of rigid and limiting. It would be like calling Pure Data limiting because it's a visual programming language. I don't know, it just seems silly to me.
There's a ton of small outfits in the Eurorack space doing really great stuff. To any one who is curious I'd suggest checking out some manufacturers like Make Noise, Mutable Instruments, ADDAC System, Modcan, and there's just too many to name.