Mathias is more of a Lord of Vampires. Gabriel is more of a Vampire Warlord. Both excel in different attributes while they cannot master the other aspects. Mathias as a tactician has planned out enemies and layout, and as that's him as a tactician and when you reach the General, he has his sword in his sheath and uses it until you defeat him. Dracula (Mathias) is basically a Wizard... who also happens to be a Vampire. Gabriel is a Warlord who has on-the-line battle experience. So Gabriel is a powerful vampire because he has those attributes. Now we know that our original bad-ass Mathias is a powerful mother-fucker indeed, but when you compare the both Vampires' trades and skills, Mathias is more of a "Lord of Darkness" like the original Bram Stoker's Dracula. While he is the strongest indeed, he is more of a general and he NEEDS his army nonetheless, he is an alchemist and a wizard on the side for his combat, and while he may have his vampiric strength in his disposal, he isn't fit for a hand to hand combat with a Belmont, that's why Dracula keeps teleporting away because he can't handle that shit. Gabriel is a tactician in terms of personal combating unlike Mathias who uses it to command armies/now his legion. Gabriel on the other hand butchered his way through the burning village, all the way through the necromancer's abyss and back to the Castle and then to the Realm of the Forgotten One's with Zobek giving descriptions such as... "He sleeps less, eats less" I mean, talk about endurance. Gabriel is a strong and mighty Vampire. Look at the trailer in how he fights off armies and their generals like "I'm my own army". Obviously this is the guy you don't want to mess with in a "last man standing". In the trailers, he fights Trevor in an equal level. He is the type that wouldn't even bother drinking vine and waiting for the whip using warrior to reach his throne room. If he senses your presence, he will fight you there and then but alas, you've MoF in which he plays as a tactician, but then look, he is a War"Lord", so why wouldn't he have his share of armies?
Both have their share of strength and weaknesses, no need to make this a Deadliest Warrior episode. In fact, Mathias would get a true Vampire friend that Leon couldn't provide. They'd be bros. Olrox would be just low-tier Vampire. They both Complement each other in various sorts. Both had somewhat the same back story. Belmonts would be nothing in front of those two.