The MIDI-piano sound comes from Suno rendering 'piano' as a generic keyboard patch. Realism needs specificity — which piano, played how, in what room.
1. Name the piano: grand piano, upright piano, felt piano — each renders differently, and all beat bare 'piano.' Felt piano is the most realistic-sounding of the three.
2. Describe the playing: expressive grand piano, dynamic, human touch, subtle timing variations — 'human touch' and 'dynamic' fight the quantized MIDI feel.
3. Put it in a room: grand piano in a small warm room, natural ambience — real pianos exist in rooms; MIDI pianos exist in voids. The room sells the realism.
4. Simplify the part. Insanely fast runs and impossible voicings scream MIDI. Real pianists play idiomatically — if your piano part couldn't be played by two hands, simplify it.
5. Exclude: synth piano, MIDI keyboard, electric piano (unless you want those).
6. The honest fallback: for a exposed solo piano piece, generate the song's structure in Suno, get the MIDI-ish piano out of the way, and record/sequence a real piano VST over it in a DAW. Suno for the song, real tools for the showcase instrument.
Good luck! Hank founder of SonorixPG