How do you detect a useless outpost ?

[Henk]

And time is scarce too. So reducing evaluation terms is important.

but if you reduce eval terms, you will never get the position rigth.

[d]3rq3/1k1r4/p1p1p3/7n/1PP3p1/4R3/4P1RK/B3Q3 w - - 0 1

for example, above, e6 is backward (general definition for a backward pawn is any pawn, the square in front of which is free, but who can not reasonably advance, because it will be lost), any advance will lose the pawn, g4 is not backward, although a single black piece supports the square in front of the pawn, while 4 enemy pieces (but of bigger value) obstruct it, b4 is also backward, although connected, as b4-b5 loses a pawn ( 2 enemy pawns stop its advance).

how many engines consider such terms?

those are objective, valid terms, and you can not substitute them for any reasonable combination of fewer terms tuned. in great many positions the game/choosing the best move is influenced by such small terms, so basically another reason why false positives migth be frequent with any eval or search patch.

as said, rigth now we are stuck.

Almost think this is something like pawn mobility for they can't move only sacrifice themselves. Nimzowitch wrote something like 'isolated d pawn is only weak in end game'. Did not have time to read it carefully.