I disagree with several of your cons to a bottom drain.
snip
Con's
Potential leakage of pipes below the ground level
If the pipes are properly installed and of decent quality, this should
never be a problem.
Maintain the pond waterlevel in strict limits
My water level can vary 15" without it being a problem. It comes down
to proper design.
Winterizing, probably more difficult.(how to empty the pipe comming from the
pond, even with a valve the upstream water could freeze)
I live in northeast Ohio where we routinely have stretches of zero and
even sub-zero temps and have not had any problem. I just keep a 25
watt bulb in the pump house to keep the temp above freezing. The pump
house lid has a piece of 2" foam insulation.

More difficult to install
Yes, but this is a one time labor, however, it eliminates a lot of
future work cleaning the pond.