Hey Dennis, Dennis here. While I agree with most everything you said, I still say no main drain, in the majority of above ground pool installations.

You have no idea how many times I have heard, "my pool is leaking, I think it's my main drain." It seldom is but always the first place suspected. That is if it is properly installed, if not, then it probably always is the cause. Thing is, there is no way of knowing.

Automatic pool cleaners do exactly the same thing, they draw water from the bottom, plus they clean the entire pool floor. They replace the need for a center drain.

There is a lot that can be done with an above ground pool, huge filter systems, multiple returns, main drains, dedicated cleaner ports and so on. It's all good if done right and maintained. But if you are at the mercy of others when it comes to keeping all this stuff working, you may want to keep it simple.