> Is this true? At my last company we wasted a bunch of time every week dealing with the accumulation of ad-hoc changes in different environments creating different behavior.

That is an issue a disciplined one-man operation won't have since (generally) they have a Dev and a Prod environment, the changes would be made in Dev first then duplicated in Prod.

If you have 2+ developers, you have environment drift like you experienced because (generally) Dev is the local environment on the laptop or otherwise a distinct environment for each developer. So now you have 3+ environments you need to sync and then discipline starts to fall apart as you have to communicate every change.