On my last run I made no conscious effort to grind at all, and out of the bosses in the storyline the only ones that gave me any difficulty were Braska's Final Aeon, and following that when you fight your own aeons. BFA took me two or three attempts but was by no means a mismatch. When I fought my own aeons their high evasion meant I could only damage them with magic and overdrives. As I had used all my overdrives on BFA, I had to use my aeons against each other or just had Lulu and Yuna casting Flare.

There weren't any fights in the game that made me need to grind. Although I'll never forget about when, after beating Sin, I flew back to Besaid for some reason not knowing about the Dark Aeons. Valefor wiped my party out with one attack and I had to do the whole fight with Sin all over again.