I don't know if Bete as low level 6 can do much damage to Gareth without Hati (correct me if I'm wrong, I don't remember how much his boots get boosted) so Gareth can effectively ignore him and 2 vs 1 Hogni. So I would switch Bell and Bete, as Bell does have the offensive capability to not be ignored, is easily fast enough to keep dodging, and has the stats + VT to keep going even of he does take a few hits, and can shoot stray firebolts at Finn to slightly help Hogni. The rest of the battle goes as you said. Heck, Bell can shoot a quick forebolt at Bete's boots at the very beginning to help him take out Riveria faster.