If I can't get that simple bolt to not leak I'll go golfing.
If you are running basic stuff then it doesn't matter. I don't care what runs for 200k miles. Any time the pressure drops from the filter like that it ain't good.
You asked, it's an extra sealing surface. Without the 90° adaptor assembly the gasket under the threaded adaptor for the sandwich plate is also covered by the other 2 gaskets.
What else matters? If the filter isn't adding longevity to the life of the engine, who cares? That's literally the only reason the oil filter is there. If your only concern is oil pressure then bypass the filter completely, the only reason for the filter is to make the bearings last longer and if you don't care about total mileage/engine longevity then it doesn't matter. I have no issues at all making more oil pressure than I even need.
Was your pressure drop comparison a long filter on a 90° adapter vs a short filter directly attached? Or was it short vs long both with the 90° adapter? Because that factory bolt and the additional distance in the 90° adaptor have to make a difference too.