These are all very interesting descriptions of how and why all-in-ones can be less efficient.
And I have never experienced any of them.
My system is an ancient, non-trendy 'mature' Braumeister all-in-one. My average mash efficiencies are always at least 83% or higher, pretty much independent of grain bill size, water volume and grist:water ratio. As improbable as that seems, I assume it is because of the bottom-up recirculation flow path of the wort during mash. Bottom-up means the grain bed is constantly being floated. Any 'compaction' takes place at the top plate 'false bottom', and decompresses with every periodic pump rest. It's a remarkably efficient system.
I got away from sparing a couple of years ago as an adaptation to low-oxygen techniques, avoiding splashing and O2 pickup from sparge water dripping from the suspended malt pipe into the wort after mashing. As
@Bobby_M said, I only loose a point or two, which for me isn't a deal breaker if I get less oxidation from HSA. I still rinse the grains with 1½~2 gallons water @ 170F (treated with sulfites) and collect the run-off in a separate bucket for use in yeast starters. If I'm too far off on final boil volume, I can add a small amount to top off. Gravity of the run-off is usually around 1.020 and alkalinity 6.0 pH or less which can be corrected with lactic acid.