Omni-Man's planet-level power and FTL speed exceed what even Iron Man's best suits can match.
Iron Man has impressive suits that have fought the Hulk, Thor, and cosmic threats. But Omni-Man operates at a consistent power level that exceeds most of Tony's standard armor. The Hulkbuster was designed specifically for the Hulk and still lost; Omni-Man fights at a comparable tier without exploiting any specific weakness.
Omni-Man's FTL combat speed is the critical problem. Even Tony's most advanced suits process information and react at superhuman but not FTL speeds. Omni-Man could potentially tear through the armor before the suit's AI registers the attack. Viltrumite combat speed simply exceeds Iron Man's defensive reaction time.
Tony's intelligence and adaptability are real advantages โ given prep time, he could develop countermeasures. But in a random encounter, the raw power and speed gap is too large for standard suits to overcome.
Iron Man's genius and adaptive suits could develop countermeasures. His energy weapons, flight, and AI-assisted combat give him tools to fight at range, and specialized suits like the Hulkbuster approach Omni-Man's power tier.
Omni-Man's FTL combat speed exceeds Iron Man's suit reaction time, and his planet-cracking strength can tear through armor designed for lesser threats. His durability means Iron Man's standard weapons barely scratch him.
Omni-Man wins through superior speed and raw power. Iron Man's technology is impressive but not enough to bridge the gap against a planet-level Viltrumite in a random encounter.
Iron Man also fights
Omni-Man also fights