I don't think it's really similar situations.
Both Castlevania I and II star Simon. He's the poster boy of the franchise and for that brief period, Castlevania was the story of Simon Belmont. With III the focus shifted to Trevor, but returned to Simon for IV. Then Rondo of Blood stars Richter Belmont, and at this point one thing is clear: Castlevania isn't the story of Simon Belmont, but rather of the Belmont clan.
Now Alucard, he was a side character in III before getting promoted to playable in SotN, and that game's popularity combined with Igarashi's influence on the series from them onwards made him a staple of the series. However, the thread that runs throughout the series remains Belmonts vs. Dracula. Many of the protagonists after SotN are Belmonts; Alucard is never playable beyond those two games. If you want to have a representative for the series, then a Belmont does the job better than Alucard, and no Belmont would go before Simon.
Resident Evil, however, is a different beast. Yes, Chris and Jill are the protagonists of RE1, but RE2 immediately changed protagonists so there's no confusion that the series is about any one character. Rather, it's about the fight against Umbrella. Leon, Jill, and Chris can each represent that just right, so they have to be judged by their own individual pros and cons. Jury's out on who has the best shot, but imo it's Leon.