I think you're confusing scenarios here. If you have known-good build, then there's no way it is compromised by regexp DOS attack - because that's the build that happened before the attack. So if you build that - setting aside the wisdom on doing that on a compromised system - the regexp DoS is not relevant. If you are building the modified code then one should definitely question why would you want to do something like that - build and deploy known compromised code.

That seems to be the root of your confusion - it's not that development system DoS is not bad, it's that if you are at the point it's possible your security is already broken in much bigger way. It's like complaining that running "rm -rf /" under root would wipe all your files and that's a DoS - without taking into account that if somebody could run commands under root on your system it's not your system anymore. It's not that wiping all the files isn't bad - it's that the reason for why the situation is bad is much earlier that that.