This is exactly what I do and it does appear to reduce the number of calls significantly - I get two or three a day between my two cell numbers and work phone but not every day. I also noticed scammers are trying to counter it by asking to press multiple keys e.g. a recent "final courtesy call about your extended car warranty" first asked to press 1 to talk to the operator, than it asked to press 3 if my car had some number of miles then it just asked to press 8 without any other prompts. So people getting to the operator seems to hurt them if they are willing to drop a certain number of potential chumps who will mess up multiple phone prompts.

Many voip services just fucking make up a number (or derive it somehow, but incorrectly) when numbers show as blocked or 'unknown' on normal lines. It's incredibly misleading and annoying, so even legitimate calls from blocked numbers get people calling some random person back.

A lot of the robocallers just play a pre-recorded message asking you to call back.

That’s when the flooding works.

A lot of the scammers are just call-centres that outsource the lead generation. By flooding the call-back number, their campaign that they paid for goes down the drain.