This all depends on what modules you use, and how many you use. But either way, you are most certainly building something with far more flexibility than a preconfigured synth. Even with just a few modules, you can vastly outperform the Sub37. Makes Noise DPO, and Make Noise Maths, with a Korgasmatron and a basic sequencer has far more capabilities than the Sub37 and for around the same price. Of course the Sub37 has a keyboard and can save your work — but if that's your main concern, you might want to think about an Analog Keys with their new Overbridge capability.
Here's the thing — and it's also a response to a previous commenter — the modular world isn't necessarily about having an easy tool to get those sounds that you like. Trust me, if you go searching for a sound, you'll find a leprechaun first. Not even the engineers of these modules can tell you exactly what is happening once you create a complex patch. So trying to find to a sound that you heard before, or are envisioning, is a very difficulty task (unless we're talking a straight up gritty bass - that's pretty easy). These things are best used as a springboard for creativity. Set up a patch without even considering what the outcome will be — close your eyes, twist some nobs and listen. You'll find a little something in there that you can build a song around. Record it and chop it up. It's like any instrument — the more you play it, the deeper you can go. I've played guitar for 25+ years, and the vast majority of my songs started out from me noodling around until I stumbled upon a nice riff. It's the same with a modular synth.
If you want the classic sounds of a Prophet or a Moog — buy those instruments. If you want a completely new world of inspiration — one that you've created yourself — build a EuroRack.
Happy Twisting!