Here me out. We all know that Wesker was an uber villain and capable to stabbing anyone in the back (both figuratively and literally), but I was on Resident Evil Wiki and I found this profile for Wesker and in it it says, "He is cold-blooded and has no qualms about betraying the people who place their faith in him." So with that being said, the only way people could actually put their "faith" in him would be to be charismatic and charming at times. People get so wrapped up in Wesker the heartless sociopath that they often forget that the main part of having sociopathic/ antisocial personality disorder IS to be charming and charismatic at times. That's how you get caught up in their trap! So, one moment the person could be cold-hearted and calculating and the next they could be schmoozing it up.
For a man like Wesker, he could easily use his intellect, looks, any of his varying occupations to place himself in a position to charm and deceive others into doing his bidding. If it were any other way, no one would have been surprised of his betrayals during the Mansion Incident and beyond.
So I'm going to continue to write Wesker the way I want. Because I know that is the correct way to portray him. Yeah, I'll continue to get people to moan and complain, "Wesker is so OCC in this story!" But those people can SUCK IT!