Just another point of comparison for you in my pond. It's a little under an acre. Fed by fairly steep 10 acres' runoff only. But lots of water comes out of the ground above it. We get big rains. I have a 12" overflow. A foot above that is the emergency spillway that is far enough to the side that it's over bedrock so it can't cut down. 2 1/2' of freeboard. Not saying my pond is perfect at all, but just another "it all depends" here.
I let my pond builder talk me out of/into things. If you've done good research, stick by your guns or find another builder. If it's someone like Otto who has a bullet-proof reputation, then best listen. A clogged overflow pipe is a crisis, so best address it. There will be floating debris as well so you'd have to take steps that way also. A large area grate/screen would be called for in either location. Bit harder to detect issues/clean near the bottom. Benefit of drawing off bottom water is valid. Though if you turn it over regularly via aeration, that argument gets weaker.
