Slitherine

I think they are too useful and spoil the Fog of War in naval engagements.
The major ships usually carried 1-5 floatplanes. The current 10-strength units are too durable, especially compared with a regular squadron with 12-15 planes.
The no-need-to-refuel trait means it is too easy to get visual confirmations of enemy ships.

I propose that floatplanes and recon planes must refuel like everybody else (ports and/or capital ships) and that floatplane strength is capped at say 3-5-strength.
In general, it would be nice to be able to set max strength for units in the editor, also for spawned units.
And be able to rename spawned units.

I've been playing around with floatplanes versus fighting planes. I've found that unless I have less than three spare air command points, that in every situation I'd prefer the combat plane. The only real advantage to the float planes is the lack of need to refuel, whereas the disadvantage of not being able to attack is just way too much of a loss. I could imagine that a scenario with only surface naval instead of air power might change my mind - especially if the float planes were used for spotting shore artillery, but then I cannot imagine a scenario with that sort of design, and it would be too much of a one-off to make it useful as a game mechanic.

However I think your idea of reduced strength has some merit. Perhaps a five strength cap would be good. It should be hard to kill in one shot (or they have no real lifetime and therefore no use), but perhaps not be 'unkillable' as they currently are since you'd just leave them alone and go kill something important instead. I'd even consider making them immune to lighter anti-aircraft units or something like that. Simulate staying high up and observing.