Quick data point that might point to some small improvements. Was looking at MAN (T2) lounges in the app, today, and found I was actually able to pre-book the Aspire Lounge for a fee of £6.00. MAN's other (likely better) lounges allow Priority and Dragon Pass holders to pre-book through their own portal, but no joy there - full on those dates unless you want to pay the full price of admission. I expect Priority and Dragon Pass holders would need to have a great deal luck just to walk up to one of these lounges to be waitlisted since every man plus dog now has some sort of lounge pass.

My Priority Pass is through an Amex Platinum card and is not the primary reason for me holding that card (Dining and Harvey Nicks credits + the occasional offer + a successful lounge visit once or twice a year get me close enough to making up for the annual fee).