When you 1st spawn as a engineer you have to charge up your repair tool. When you get revived you have fully charged repair tool, meaning 3 engineers can easily rush and use this to their advantage against any oncoming force.
That's not entirely correct. You spawn with the fully-charged repair tool. Only when you swap classes or skills on-the-fly (at barracks, armory or flags) you will need to recharge it. Yep, this definitely needs to be fixed. Well, not ANY oncoming force. If your 3 engineers bunch up closely together, a mine or an HE shell will take care of the problem.
i agree, using teamwork to win should not be allowed, nerf But seriously, 3 engies using revive is easily stopped, not quite as easy as 3 engineers not using revive and building a ref, but near enough no effective vehiclecounters for instance, and as theBlind said, a BE rifleman will make short work of 3 engineers, unless he sucks :D