Well... as far as Samus vs MC here... Look, they're both good warriors, but Samus's gun so powerful...her armour is made of the best material in the known universe, not just what mankind knows. It'd be like shooting a frieght train with a pellet gun... MC's weapons are practically useless against her. It'd be like sticking a Grunt from the stone age against the MC...
Now, Vincent vs MC...
Option 1: MC's Resistance to Projectile Weapons
Who said Legendary was canon? It's closer than the other difficulties, canon would be closer to Legendary or Heroic, but none of them are going to be perfect. I mean, an Elite taking 5 .50 caliber shots to the face? Or being hit by a high-explosive rocket? No... Wont work. Besides, in the Halo game all you can do is jog and duck. Your not very agile...
The Master Chief's armour as well as shields work better against projectile weapons than they do energy weapons, therefore his resistance to bullets is very high. He's survived dozenz of rounds from machine guns, sniper rifles. He was shot at by a Jet which used a missile to take him down and he dodged that, and survived the blast and close proximity. So, it'd take many bullets to break through both his shields AND his armour, and you'd have to hit the same spot more than once to do that. His armour isn't a piece of shit, it's designed to keep him alive.
2. MC Ability to Dodge Bullets
Simply put the Master Chief couldn't dodge a bullet travelling at hyper-sonic speeds if he noticed it after it was fired at him. However, he's very, very good at estimating it's trajectory and taking the appropriate maneuvers to get out of the way. He's fast, agile, and his reflexes are nearly instant. Plus he's been trained intensively since he was about 6. He knows HOW to move in the right ways to throw someones aim off in the most efficient fashion. He'd be trained a lot more heavily than a modern SEAL so he wouldn't just stand there and take bullets.
He was surrounded by eight ODST from the Helljumper divisons. The best troops in the UNSC. That's several trillion people... ODST are a lot like SEALS in ways. They're the best soldiers a normal human could give you. He was unarmed, and survived the encounter, dodging most of their bullets. Eight people...best trained, I think they had fully automatic weapons. That speaks for his ability to dodge a bullet. Also, he dodged a missile from a supersonic jet...
3. MC's ability to Shoot...
I dont play much final fantasy, most of what I know of vincent is what I saw from advent children. The movie my friends made me watch... I dunno. He seems very agile, dodging several attacks, with a mild ability to fly, or at least substantially lower the gravitational effects of gravity. So I expect he'd be able to dodge a fair amount of bullets himself... However, the MC's training, and genetic enhancements, combined with the increased ratio of performance would make his ability to shoot pretty high. I mean, he can hold is muscles perfectly steady and his eyes sight is very, very high. He'd hit more than he would miss I'd think.
Hand-to-hand, I'm not sure of Vincents total technique, but I know the MC's skill in martial arts is also, very high. Combined with enhancements to increase learining process and physical ability... Being inside MJOLNIR to vastly increase his speed and reactions to equal this thoughts. If he hit Vincent at all it'd hurt...