It's not a matter of them not being able to make good music without El-P. It's a matter of it not being real Cannibal Ox without him. As far as I'm concerned El-P was as much a part of that group as Vast and Vordul. And by far the most important part at it. He made them sound like they did.
They can still make a good album without him. It'll just be like their solo albums though. Good enough music but nothing special. I'm personally not the slightest bit excited about it. I have no doubt I'll completely forget about it and only ever check it out if I happen to hear about it after it drops.