I think it is mainly used to describe a negative way of riding to begin with. I don't think the term is generally used for a rider who is unable to take over, suffering in the wheel.
I also think a lot is perception and comes down to "status" or "hierarchy". If tomorrow Evenepoel goes in the attack, and he gets Ivan Sosa with him, yet he refuses to take over and lets Sosa do all the work, it will be considered wheelsucking, and rightfully so. If the order is reversed, and Sosa doesn't come out of Evenepoel's wheel, a lot less people will see it as an issue.