I believe the main issue of all this was how a strong bond meant squat to Mega Evolution when someone as disjointed as Nurse Joy and her Audino managed to pull that off so easily, despite their bond being a huuuuuuuuuge mess. Power control was not the issue. Evolving at all was the issue. This is the anime that likes shoving friendships down our throats, after all.
I already explained that tho.
First, they did share a strong bond, regardless of the bickering. That was the entire point of the episode and Professor Sycamore explicitly said himself that they shared a strong bond, despite fighting a lot.
Second, Audino only did it for a couple of seconds and it was a very extreme situation. It is not that hard to believe that even a Pokémon and a Trainer with an imperfect bond would still be able to mega evolve for a couple of seconds if the situation required. Besides, no bond is perfect anyway, the requirement for mega evolving is a
strong bond, not a perfect bond.
I think the problem is that you think two characters can't share a strong bond if they fight a lot, which is not true at all. We fight because we care. Fighting is a way to express our feelings and views to the other people, and storing that anger is not a good thing because it will eventually become too much for the person to handle and come out all at once. Not to mention you start resenting the person for all the times you were angry but didn't say so. Of course there are limits to that, such as when a relationship becomes toxic, but fighting alone is not the issue, not being able to overcome a fight you had with your friend and grow from it is.
If anything, Joy and Audino's bond was one of the more realistic ones we have seen in the anime.