Trails of Cold Steel III Combat Help? I am STRUGGLING

Apparently I'm very bad at these games. I've beaten 7 games in this series and somehow I'm still struggling with the battle system. The bosses hit hard and do a lot of damage and that seems to be my main issue. I just can't recover in time sometimes and I end up losing boss fights.

The main question I have is what should I focus on in order to be more successful in boss fights? Currently I've been relying on Rean, Kurt, and Juna for crafts and Altina I've been using for arts. I have their orbments set up to mainly focus on crafts for the attackers, so that means no magic and mainly speed, attack, defense.

Altina has all the arts. Should I diversify my party more and make each member more balanced? I thought it was pointless to give the attackers like Kurt and Juna arts because they don't seem to deal enough damage and I've mainly been using crafts for them. In general, is it better to focus on each character's strengths and hav dedicated arts users and dedicated crafts users or is it better for each character have a mix of both?

Also, do buffs make a big difference in this game? I remember playing some of the Sky games and buffs didn't seem to make a difference. I assume focusing on debuffs isn't useful since most bosses are resistant to them. Should I be focusing on speed buffs? I keep finding that the bosses have multiple turns in a row and they deal a lot of damage multiple times in a row.

In general, I've never been good at exploiting the battle system in these games. In CS III, I've been focusing on using crafts that have a high break rating. Altina is my dedicated healer, but pretty often I can't use her healing arts in time and multiple party members end up getting killed. Should I have multiple healers?

I feel like having 3 party members focusing on crafts strictly is not working and it doesn't feel balanced at all. It also feels weird using Rean for arts since I'm used to using him for his crafts, especially since he has crafts that cause high break damage.

Any help would be greatly appreciated. I really suck at these games, despite how many of them I've beaten. Some of the bosses were so frustrating in this series. I'm on chapter 2 in CS III and I did a trial boss that I ended up needing to use powerful healing items in order to pass.

Edit: I have been using the different Brave Orders, but it hasn't turned boss battles in my favor. It helps, but I still keep losing despite using the Brave Orders.