The biggest difference is that neither Glaz nor Finka have the ability to force you into that kind of 1v1. With Blitz, he can generally push you like a moron with little to no risk to himself. Aim for his feet to chip away at his health, and you'll get shot to death when he aims. Aim for his head, and he has a free pass to push right up in your face.
I've never had much of an issue with Glaz, but Finka and Blackbeard are two comparable ops to Blitz imo. However, they can't force you to deal with them without using some strategy. For instance, you can just refrain from peeking a window that Blackbeard is rappelling on, but you have to deal with him if the defused is planting in his line of sight. Blitz requires no such strategy. By simply running at you, he forces you to deal with him immediately, or die.
Finally, when did it become okay for someone's operator to solely decide who should win in 1v1s? It should never be a "I'm a half competent blitz so I win" scenario. Ops whose stole purpose is to get kills and nothing else is just lazy design, and Blitz, Finka, and Blackbeard are just the epitome of that. Imagine, if Blitz was added into the game today, he would be considered one of the worst designed operators to have been added since launch.