Is Alexander supposed to be strong or not?

[spukrian]

That or he actually believes that Alexander is old and weak?

Daniel might not have understood that Alexander isn't human then, or even until near the end as it only hints at the fact throughout the game

Well, that's possible. Just got the feeling that Daniel was trying to trick himself. He's a bit of an unreliable narrator.

Anyway, Alexander had some sort of supernatural powers/knowledge and would surely use this to his advantage if he had to fight Daniel.