Blocking things with construction sites has limits put on it by rules. If people were breaking the rules, then they should have been screenshotted and reported for banning. Healing tents and forward spawns are very useful. Weapons racks were also very useful, especially for engineers who relied on them to build everything else.
You can't seriously tell me that an engineer building any of these things was contributing less than any peasant. IMO they are contributing much more, and once they have set up an area, they can defend it viciously with their throwing skills + infinite ammo. The weakness in this comes if you catch them setting up. Placement of siege weaponry is (was) a very important facet of this class, and one that required knowledge of the map layouts and common defensive/offensive areas.
I've played on over a dozen different characters, from cav to xbow/2h and everything in between. Engineering was honestly the most fun that I had of any of the classes. You don't get as many kills, but you really feel like you're helping the team, especially if the team cooperates. Unfortunately I never got a chance to play much of it before it got erased from the game. Still, I hope that weapons racks come back with some kind of c-site limit, and that forward spawns come back with the spawns resetting every round.