How is it any less of a tactic if people just attacked the bomb planters with non DoT attacks and die afterward?
Unless players can stealth, there really isn't much places to hide and wait for a good time to attack, which would be the same as just attacking outright after spawn to avoid losing the doors.
Its bad enough that the defenders have to wait to exit the spawn while attackers get to run straight to the doors upon spawn, now DoTs can't be use to hold the enemy down till the spawn lets defenders exit.