Me, two weeks ago, adding yet another function onto an increasingly complex webservice: "hey uh this is getting pretty confusing, why don't we structure the request this other way so at least it makes more sense."

Manager: "just leave it as is, let the other team worry about how confusing it is. It's their problem now, I want you to move on to a new assignment."

Now- the other team is confused by the webservice and does the requests wrong, resulting in failures. Does it become my problem again when they report that my webservice isn't working?

Yes, it does.