I'm just going to chime in that nothing about this sounds like a better origin story for Dracula than what Lament offered. Mathias' deeds were motivated by an actual, relatable event in his life, the death of his wife, which presumably changed his entire worldview about life and the religion he used to follow. He became warped enough to orchestrate his masterplan, callously destroying the life of his former best friend in the process, not because of some magical Macguffin that arbitrarily made him evil, but because of pure psychological trauma. Vampirization was just a means to an end, that being attaining power to mock God, that he craved after he lost everything that mattered to him.
Except he then goes into hiding because it's only God he hates, not people. At least until people kill his next wife.
Mathias is extremely intelligent, but he's also just insane. He tricks his best friend into killing his own wife and then thinks that offering him immortality will make them even? What?
Lament has a pretty corny presentation about it sometimes, but this is a compelling, reasonable sequence of events that lead to a man becoming Demon King. It even aptly sets up the Belmonts vs. Dracula blood feud in that Leon is essentially put through the same tragedy as Mathias, but his faith and humanity is never shaken. Two men irreconcilably separated and at odds with each other through a difference of character and moral fibre.
The problem I have with Lament is that I don't see that. Mathias only comes on stage at the end for a "Hi, I'm going to be Dracula, and this is all because of me" before leaving.
All I see in Gabriel is a bumbling, clueless would-do-gooder who's whisked from one situation to the next, manipulated by each and every member of the cast until circumstances just decree that oh, he's going to become Dracula now. He's never characterized as malicious in any way, in fact as much as the game's schizophrenic writing indicates, he's always motivated by good intentions. Even his final vampirization or who-knows-what-really in Reverie happens because he's guilt-tripped into SAVING THE WORLD by Laura. And not that I've seen Resurrection's events for myself yet, but it sure sounds like there's pretty much nothing there to push him into becoming the sort of dark lord they're trying to pass him off as later on. Feeling guilty about Marie's death doesn't make for a good reason when it was purely Zobek's doing, and he was forgiven anyway.
Um... couple of problems.
-Gabriel doesn't care about right or wrong. He just wants his wife back. He spends the game sleep deprived and running on adrenaline.
-After saving the world and finding out that he was being manipulated by everyone, Gabriel also finds out that he can never have her back and has to go on without her.
-He ends up despondent and nihilistic. He no longer believes that he has choice. That he's just a puppet.
-When he drains Laura it isn't because he's been guilted into it, but because he knows that he has nothing left and doesn't feel that his life is his own due to him being manipulated so much. He goes so far as to blame God.
-Finally, he becomes Dracula in his mindset because of drinking vampire blood. It burns out whatever goodness was in him. So suddenly that darkness that was rising to the surface through the whole game is completely unhindered.
There's just no practical or sensible reason for him to become a villain, which without question is the part Dracula should play in this series, positive or sympathetic character traits or not. If the intention is that after Lords he just wallows in self-pity for a millenia as a mopey recluse, that would fit the character arc, but what kind of Dracula is that, then? A pretty boring one! The alternative option is to make him a warring dark lord whose character does not justify or set up his behaviour, so they've pretty much written Gabriel Belmont Dracula into an irredeemably stupid existence.
Gabriel suffered numerous trials and struggles, and gave up everything, including his humanity, in the process. This cost him everything he loved and cared about, and even cost him his soul. In doing this, though, he becomes something far worse than any of the Lords of Shadow, and something far more powerful and terrifying. We actually get to see this fall.
Mathias is mostly understood through 5 minutes of conversation and a blurb in a manual or two. He lacks a lot of depth. And is evil and power grabbing seemingly for rather petty reasons. God killed my wife so I'm going to live for eternity by killing innocents! A couple of frightened villagers killed my wife so all humans have to die!
Gabriel becomes his dark self cleansed of human emotion and compassion, and not because he wanted to but because it had to be done. Mathias, on the other hand, is driven mad by the death of the woman he loved, then mellowed for a few centuries after getting his hands on the Macguffin of Never Mentioned Again, then remembers that he's evil when his other wife get's killed. Gabriel is terrifying. Mathias has no sense of proportion.
I suggest seeing the end of Gabriel's transformation before trying to draw a direct comparison. How he is as Dracula in 1022 is very different from 20XX, considering the weight and weariness that 1000 years puts on a man.