in terms of "preparing for the final battle", i haven't used a healer either time i went, nor a mage at all the first time. i had a lot more trouble the second time, partly because whatever i did in the story made the boss harder, but also because the first time urpina sparked some kind of ultimate attack that pretty much blew out one of his entire lifebars in a single turn. the second time i was reliant (for one form) on receiving a healing benison at a certain point, but it would always happen since my party would dip below a certain amount without fail on the same turn every time. except then i ground for a while and got a different benison as the likely one, so then i had to go back and get the healing one again. which was easier than i thought it would be.
i will say there are a lot of systems in SGA and you won't be forced to maximize across all of them to win. (that is to say, to the extent i used the benison to win last time...it represents other things i didn't worry about. because i knew it would happen.) there's a certain element of trial-and-error in difficult boss fights, for all of the post-gb saga games i've played, since you'll learn things you can and can't count on happening, and i feel the games have always encouraged it (RS2's final boss maybe less so because kitting out the party with so many passives is relatively important) because the spark system often represents that final trump card that pushes you to a victory. the combination of experimenting for a while and then receiving that final piece often represents the win and it's something i really love about the games, and since in this game the spark is also just a bonus turn, it's very powerful.
but also yes stuns are ridiculous and attack and defense debuffs are also quite effective against the final boss, particularly if you already have an axe user you've raised all game. which might not be true this time, but will probably eventually be true.
i will say there are a lot of systems in SGA and you won't be forced to maximize across all of them to win. (that is to say, to the extent i used the benison to win last time...it represents other things i didn't worry about. because i knew it would happen.) there's a certain element of trial-and-error in difficult boss fights, for all of the post-gb saga games i've played, since you'll learn things you can and can't count on happening, and i feel the games have always encouraged it (RS2's final boss maybe less so because kitting out the party with so many passives is relatively important) because the spark system often represents that final trump card that pushes you to a victory. the combination of experimenting for a while and then receiving that final piece often represents the win and it's something i really love about the games, and since in this game the spark is also just a bonus turn, it's very powerful.
but also yes stuns are ridiculous and attack and defense debuffs are also quite effective against the final boss, particularly if you already have an axe user you've raised all game. which might not be true this time, but will probably eventually be true.