I don't doubt that a bad looking bike isn't the biggest deterent. But it's the combination of factors that's practically helpful.

A tatty bike with 2 (or even 3!) high quality locks is a much lower target than a half decent looking bike with just a single cheap lock.

The more opportunistic the thief, the better your chances of not getting your bike stolen if you have 2 more locks than everyone around you. Heck, I'd argue, due to their unusual nature of being (not) used as a lock, a dozen zip ties might be more effective than a 3rd of 4th lock, simply because no thief is expecting to encounter it. They want a quick getaway, spending 20 seconds per tie * 10 ties is likely much longer than what it's worth for them, especially if your bike isn't that nice.