The problem here is that what you see as “brainless” you might not actually realize how much they are actually helping, especially when they are properly sandbagging windows (sandbag in window then another on the floor behind it, creating a raised shooting position with more cover) OR blocking windows that are getting targeted by tanks.
Just because they blocked off the largest point of entrance out front doesn’t mean they’ve blocked everything. Stopping enemies coming straight into the point is usually a good thing.
Sure, some people need more practice, or an actual lesson in engineering tactics, but I honestly think run-and-gun players make a bigger deal out of it than what it is and breaking down indiscriminately, causing engineer players to retaliate and start dumping wire everywhere.