You are absolutely correct.Because, in the tropes of superheroics, you don't get to say no to destiny. With great power comes great responsibility. Buffy certainly didn't, that was the whole point of both the movie and season 1.
However, Tropes are tools used to very quickly communicate common but complicated ideas.
So, if the standard superhero tropes work for your story, you should use them.
If they don't work for your story, ignore them.
One of my favorite series is THE BOYS which does an awesome job of subverting (or proving - depending on one's point of view) every superhero trope in existance.
Buffy's story is so messed up that I don't think the normal superhero tropes could really apply. Plus, Whedon was so totally into subverting everything possible that I think he often wrote Buffy to counter the superhero tropes.
On the consent issue:
1. It is a serious issue, in general.
2. I don't believe it mattered here.
Why?
None of the New Slayers were required to fight. The Potentials at Buffy's house were given a choice. The other Potentials were given superpowers.
Problematic? Absolutely. As @AlphaFoxtrot notes, Dana is a result.
Wrong? That depends on the girl and what she does with her new superpowers.
Unfair? Again, depends on the girl and what she does with her new superpowers.
I would hope that as Buffy and Giles rebuilt the Council, the focus would be on what was best for the Slayers as well as fighting the forces of darkness.