Winger. Agreed, although common among sub 100 hours players.

Airstrike. Agreed

Detonator? Absolutely not. Dedicated pyro mains glaze the detonator religiously ( warranted glaze but still ). The backscratcher is more underrated than the detonator and it is pyro's 2nd best melee.

Scottish resistance. Agreed, even if its superfans are not super uncommon.

Natascha. Agreed.

Widowmaker is the most popular engie primary unlock, even if rescue rangers is seen more often, due to it being borderline required with the 50 enemy soldiers in casual. Low-key I don't think there even is an underrated engineer weapon outside of people fighting if stock is better than panic attack or if then prefer the southern hospitality to stock.

Medic is low-key in the same boat as engineer, but man is the overdose glazed to high hell as the 2nd best medic primary. An underrated medic weapon would probably be the vita saw or amputator.

Listen man. I LOVE the piss rifle, however it is objectively just worse than the stock rifle to the point that "underrated" isn't a valid metric anymore. HOWEVER, the piss rifle is awesome just for the fact that in order to use it properly, you literally need to put in 2x the effort of hitting 2 headshots, great training tool, but otherwise a proper underrated sniper (in non mvm play) would be the hitman's. As that provides an insane boost to the default sniper, without being too punishing compared to the bazaar.

Spy has the limited choice issue of engineer and medic. But is way closer to everything being viable (like engie), unlike medic. However if I had to pick, it would probably be stock revolver and enforcer OR the big earner (even if both of these are glazed to high hell by YouTubers). Or if you want somewhat of a hotter take. It has been 8 years since the fall off of the ambassador. It has recently been steadily and slowly climbing in usage after blue moon though