We're not good on the river 1/5 of the time here?

IMHO, the hands that seem to make most sense for MP are Ax (including Axh).

Board: 7h 9h Ad Kh Kc
Dead:

equity (%) win (%) tie (%)
Hand 1: 75.0000 % 50.00% 25.00% { A2s+, A5o+ }
Hand 2: 25.0000 % 00.00% 25.00% { As9c }

He certainly could have other hands that beat us, but are there really enough to make this a fold? Keep in mind that a lot of low made flushes bet the turn and most sets raise flop/bet turn.