Yes, that is correct- just like how in Strange [SPOILER ALERT], it is the death of the Ancient One and her last words she imparted on to him of which compelled him to become a greater person, also being that her death is directly what motivates and inspires our protagonist.
And yes, while other Marvel films don't necessarily need to have the death of a mentor figure- some of them, like Guardians, not necessitating this role be filled in any capacity. It would be simple to draw parallels to Iron Man and Ant Man, but honestly, the slight subversion of how the movie handled the typical archetypal story allowed for it to be enjoyed whereas with Strange, the differences are only cosmetic.
While it is only natural to see that the Hero's Journey is archetypal in its structure, and can be an inevitable similarity- I feel that it should be the duty of Marvel to rethink the way these stories are told, and to shift the producer centric strategy to a more director oriented approach. I mean, Batman Begins is still a hero's journey, but it in no way shape or form feels like Iron Man or any other Marvel Film- it feels like a Christopher Nolan film.
I think that with the sheer volume of films that Marvel is producing, and to the fact that they can basically print money- I'm wishing that they would be more adventurous as to NOT do a typical story, and to instead try a riskier move with more innovative and dynamic storytelling. I also understand how easy it is to be lost in the fact that this film is an Origin Story, and can therefore be justified in being this archetypal- or how archetypal the Hero's journey normally is, yet when a studio constantly puts out 2-3 films a year, of which, so many similarities can be drawn between each of their films- it stops being entertaining, because it stops being surprising.
I don't hate Marvel, I just hate that they're not more adventurous with their programming. My fear from Marvel is that they are so set in their way of storytelling that we'play never get something on the caliber of The Dark Knight, because there isn't enough creativity and drive to want to achieve that.