> we cannot manually fix some minor mistakes of ours when creating resources because that'll mess up terraform

In my opinion if you're doing manual fixes you're doing it wrong. Let's say you do your manual fix in your Dev environment. Do you remember to do it in Prod/whatever other environments you have? Are you sure you did the EXACT same thing? Did you change 5 other things trying to fix it first?

You end up with so many different deployment environments that are unique 'snowflakes', and when something breaks in one it might not affect the others cause they're in totally different states.

It's a nightmare.

In my opinion, infrastructure as code is the only way to do it in a serious environment.