They are both possibilities that depend on the numerical strength of attacker or defenders. Not contradictions.
Have you ever been struggling to get up and into the fight with lots and lots of enemy fighters over the base, maybe getting killed a lot, and actually said to yourself, "Man, I wish some toolshedders would drop the FHs and save me from myself?" I think not.
Thus the "Your idea is bad because vulching is bad!" argument holds no water.
The "It would make the defense too strong!" argument isn't inherently stupid like the "bad vulchers!" complaint, but it is very debatable. I know that if the attackers are having to suppress defenders up until the minute troops go then by definition combat is occurring. I know that if there are people willing to up from the base and defend but cannot, combat is being impeded. It is logically inarguable.
Some people seem to be saying "Oh, but it will be very difficult to take a base if there are more defenders than attackers!". Seems to me that result is natural if offense and defense are actually in balance, and a different result occurring a large percentage of the time is a sign something is not well balanced.