I always figured Angeal was pretty damn strong. I mean, look at the flashback to the three Jenova subjects training together. At one point, Sephiroth casually blocks a combined strike from Angeal and Genesis with one freaking hand. Then later, when Sephiroth and Genesis get serious and might kill each other, Angeal blocks a strike from the Masamune and a swing of Genesis' Rapier at the same time.
That's fucking hardcore, dude. Sure, it's only one instance to go by, but its still very impressive to me.
Now, on the subject of Zack's death. I liked his final talk with Cloud. Keep in mind that despite Cloud finding the strength to crawl to Zack's side, he still mostly looks totally out of it as Zack talks. Zack is still taking it on faith that Cloud could recover and live up to the whole "Living Legacy" thing. With no way of knowing if it would really happen, or if Cloud would just kind of lay back down next to him and die of exposure/starvation/dehydration. I liked it when Zack brought it up at the end of ACC, and Cloud cuts him off "I know, I'm your living legacy." It was like, such a validation for the poor guy to hear that, Cloud remembers what I did for him.
As for the bit with Zack's spirit... that also speaks of Angeal's strength to me honestly, though in a different capacity. It shows Angeal's white feathers, and his hand reaching out to Zack as he moves on from his dead body. If this was not just some dying hallucination of Zack's (which I considered possible since it's totally unlike any other journey to the lifestream we've seen, especially considering he seems to head for the sky for some odd reason) then Angeal has been holding onto himself, not dissolving into the swell of consciousness around him, for more than four years. Since he's not a Cetra, and he didn't focus his whole being into hatred like Sephiroth did in order to accomplish this same thing, then he must've had some impressive mental skills.