Why is steaming-hot sushi rice wrong for nigiri, even though cold rice is also bad?

Answer: Steaming-hot rice makes the fish warm and the rice sticky, ruining the bite.

Steaming-hot rice makes the fish warm and the rice sticky, ruining the bite. ✓ — Right. Sushi rice is meant to be served at body temperature, not piping hot. When rice is steaming hot, it warms the fish on top and turns gummy and sticky, so the piece loses its clean, balanced bite. Cold rice is bad because it feels hard and dull, but hot rice fails in the opposite way.

Steaming-hot rice makes the fish and rice contrast too sharp. — Not quite. A slight contrast between warm rice and cool fish can be pleasant, but steaming-hot rice pushes that contrast to an extreme. The result is a jarring bite where the hot rice overwhelms the delicate fish instead of blending with it. The goal is a gentle warmth, not a dramatic temperature clash.

Steaming-hot rice releases all the aromas at once, which is too intense. — No. Heat does release more aroma, but it doesn't unlock every smell and taste at once, and the real problem with steaming-hot rice isn't intensity of aroma. It's that the heat damages the texture and warms the fish. Aroma is a minor factor here; the main issue is the ruined bite.