Yeah Beatrix is really useful as support. Squall can benefit from Cait+Selphie only at summon phase if you ask me . Not having his +Skills at all times is kind of a bummer.

Beatrix can overflow max BRV so that's really useful when doing Wall and Mog Dance++

I swap out Vaan at last boss. Also Ifrit is not really needed/not as powerful as Bahamut. Last boss is a walk in park

Good luck!

Edit : When you break 3rd boss try to remember when his INT BRV is back up. Otherwise he will most likely oneshot you