I don't think that's entirely true. It comes up pretty often. You may not be doing formal proofs but it's helpful to have a thorough understanding as it helps guide intuition around scaling your product (e.g. how a database query will scale with more users). It should influence your design early on rather than be something requiring a PHD consultant later on

I deal with this stuff regularly, but not daily. I'm sort of the go to guy on the team when things start to feel CS'y. It isn't PhD level stuff.