Steve backscales from 3.53 tons, Roy upscales from 3.14 tons, I think Roy would have the AP advantage though not by too much.
Dunno much about Roy so I'm going off of the profile... Roy really doesn't bring anything to the table in his High 8-C key, he's literally just a swordsman. Steve should have his fair share of battles by iron tier, so he should be skilled in swordsmanship as well to keep up with Roy.
And since swordsmanship is all Roy brings to the table, he's in some real trouble. Assuming the scenarios where the fight stays in melee and their swordsmanship experience is comparable, Roy's AP advantage isn't guaranteed to help him against someone like Steve's hilariously enormous lifting strength advantage, along with s shield that stands unphased by at least 8-B attacks. On top of that, Steve has a massive Mid-level regen rate at his peak physical condition, and it's perfectly possible to have golden apples during the Iron tier stage of Minecraft, increasing his already large natural healing advantage. Potion use will be unlikely, since Steve will only have gotten potions from looting places (in order for Steve to have his own personal custom potions, he needs to craft a nether portal and find a nether fortress to farm blaze powder. Not only will you need a diamond pickaxe to make a nether portal the official way, but in a nether fortress diamonds are a fairly common loot to find, implying Steve would be diamond tier at that point). Therefore, the amount of actual potions Steve will use in the game are more improbable than anything, and potions shouldn't be a reliable wincon.
Iron Golems and Snow Golems only attack entities considered hostile. They are not slaves to Steve and they will not fight for him.
Ender pearls would be useful if used strategically, considering the damage they do early on without a reliable source of protection and feather falling enchants.
Honestly, the only reliable source of weapons Steve would have at this time is a sword, an axe, a shield, bow and arrows, and flint and steel.
That being said, I'll give it to Steve due to his physical stats making it too difficult for Roy to overwhelm Steve, despite his AP advantage. He can recover from damage quickly, unlike Roy, and on top of that, Steve has the range advantage with bow shots, giving him a good percentage of wincons should he choose to fight range, which he can at any time with the use of enderpearls. Those enderpearls can also help with temporarily getting out of the heat of battle to recover with golden apples if necessary.
Steve for Regen and Versatility.