That's how we do things at work. If we need to change a class function we outright copy/paste it then change what we need. This is so everything is backwards compatible. A bug in one version might be expected or documented in a previous. We can't fix the bug in an older version unless we get the OK from our clients because they might be depending/expecting it for their code to run correctly

It's a good system. You shouldn't complain. And deleting code is easy since not everything depends on everything