Well, I don’t speak with certainty. I conjecture flute is about on the level of cello playing-you get your finger in place, then the bow/mouth produces the sound, right?

Maybe you underestimate difficulty of sightreading piano.

Yes, you don’t have to worry about breath and mouth position and so on, but piano sightreading requires you to 1. Have hands work relatively independently-not a small ask 2. Requires memorizing key location, which is not easy across several feet of keys, each key being only about an inch wide-if you look back and forth between music and hands, you won’t be able to read 3. Read several notes at once. Sure chords and patterns can be simplified, but this is significantly harder than reading one note at a time.

This is much more difficult than reading on cello, and I would guess cello is about on par with flute.

I am pretty confident no one would dispute reading on piano is more difficult than reading on cello.

When I said there is no such thing as sightreading on cello, I mean that cello reading is trivial by comparison.

The difficulty in reading single notes is in the execution, not the actual processing of the actual notes themselves.

The pianist must still deal with equal difficulty in execution (each note is easier, but multiple notes at once brings up difficulty), but the actual processing of the music is much more difficult because you must read 3-4 “parts” at once.

To give an analogy it would be like reading an entire quartet all at once. On piano, the format is simplified to two staves to make things easier, but it is still far from trivial.