Iron Man's suit provides overwhelming firepower that keeps Deadpool permanently suppressed.
Deadpool can't die, but Iron Man's suit can suppress him indefinitely. Repulsor beams, sustained uni-beam heat, and missile systems can keep Wade in a permanent state of 'regenerating from the last attack.' Tony can also fly, meaning Deadpool's melee weapons are useless.
Tony's biggest advantage is containment โ he could freeze Deadpool, seal him in reinforced materials, or simply fly Wade into the stratosphere and drop him. Wade survives all of this but can't meaningfully fight back.
Deadpool's fourth-wall awareness and chaos factor are his only real assets. He might annoy Tony into making a mistake, but Iron Man's AI handles targeting independently of Tony's emotional state.
Deadpool can't die. His unpredictability could exploit gaps in Tony's AI targeting. His weapons could damage the suit if Tony gets careless at close range.
The suit provides flight, ranged weapons, and containment options that Deadpool can't counter. Tony can suppress Wade indefinitely without ever entering melee range.
Iron Man wins through technological superiority. Deadpool survives but can't threaten someone who flies above his effective range and has energy weapons.
Deadpool also fights
Iron Man also fights