OP here...
I've been trying some of the suggestions and not having much luck. I may just be expecting too much from side discharge and a very fast growing lawn. I've tried slowing down (almost to a crawl on the cut, which makes an acre take a looong time), mowing more frequently, even lifting the chute, all without much change. I'm at 3.25" cutting height, I cut dry, there is absolutely no build-up under the deck, chute is not clogged, blades are sharp (original blades).
I've attached some pictures. First a look at the clippings, second one a look at what I'm cutting.
This is a cut after 4 days; I'll cut again in 3. There's just no way I can cut any more frequently than that. Need to find a way to slow the grass down and still have it look green.
I can't believe it's the equipment, but I see the pros cut similar lots in my neck of the woods (with Exmark Laser Zs mostly) and they don't leave this behind. And they don't look like they're double cutting.