Fal ‘Chavamee is a badass, and seemingly one of the best Sangheili swordsmen in existence. I don’t think he achieved the rank of Arbiter by winning a raffle, and as we know, most Arbiters are on par with the best Spartans. The Master Chief is obviously a badass, with near immediate reaction time, he’s far faster and far stronger than any normal human, and this is only increased by his Mjolnir.
given the fact that your average Elite is very much capable of killing a Spartan, I don’t think this fight would be very one sided. The difference in weaponry would play a big part, I think giving Chief a sniper rifle does put Fal at a massive disadvantage.
If Fal was able to get relatively close to The Master Chief, I truly and honestly believe the fight could go either way. The victor will not walk away unscathed.