Is ATC really responsible for terrain separation? I was under the impression they can advise you when your altitude looks odd, but you are still responsible for avoiding terrain by following procedures and sticking to minimum altitudes, etc.
As the pilot you are required to follow the instruction but ATC aren’t responsible for you not doing so.
There are situations where you may inadvertently lose communications, so ATC can’t tell you to climb for some future higher altitude requirement. In this case the pilot needs to climb and fly the minimum for the area they are in or airway they are following.