@Kafriel
Thank you for your feedback
1) Although it is true that most FT battles are largely decided by magical power, certain characters do possess a large amount of physical strength that in most cases, they wouldn't even bother using their magic against an inferior opposition. Example: Gildarts is able to toss Natsu onto the ceiling just by flicking his arm. I'd imagine the likes of him can solely rely on their physical strength against average or below average level mages (Natsu being an above average mage).
And then we have characters like Makarov who utilize magical power for the sole purpose of attaining a tremendous amount of physical strength (Titan form). So although it may not be used directly, physical strength is indeed used by some character's for offense purposes. I'd say we just leave it in?
2) Every one can take hits, but
how many hits can they take is the question here. Durability tries to cover that. For example, Lucy will most likely get K.O.ed after getting hit by Gajeel's Iron Dragon Roar, Natsu on the other hand, is more than likely to eat at least a few before going down. So Natsu is more durable than Lucy.
Stamina in Fairy-verse does largely depend on the amount of magic that one has access to. Since magic is used to cast spells, a greater amount of magic implies a greater stamina (ability to fight for a prolonged periods of time). "Magic" is akin to "Ki/Energy" in Fairy-verse, since it is shown that running out of magic takes its toll on someone, rendering them unable to walk in extreme cases. Moreover, taking away someone's magic fast enough, and they'll be incapacitated for a prolonged period of time, and may even die (Example: Aria vs. Makarov).
We could re-word the terminology for it to reflect this. "Stamina" to "Magical Capacity", or just "Magic"? But we'd be ignoring other factors that may affect Stamina such as physical conditioning, age, and the ability to absorb magic by certain characters.
To summarize: Durability is how well someone
handles damage, while Stamina is
how long can someone fight for in battle.
As for Defense, other characters such as Millianna and Yuki possess magic deflecting/nullifying abilities, while Gildarts is able to disassemble any spell. Ultear on the other hand, is able to fast-forward or reverse time which allows her to pretty much render any magical spells useless. There are many more examples of defensive abilities. So it really isn't that rare of a trait.
3) I don't see anything wrong with accounting for magical diversity in both Offense & Intelligence