I realised the key to the final stage is to figure out which of my heroes' special skills are most suitable. In my case I definitely needed Jolly, but he is too slow to recharge, so I put him next to Ludwig. The combination of Jolly, Ludwig and Dawn helped keep my damage dealers alive long enough to kill off the final boss.
Previously when I didn't use Jolly, my team usually suffered at least 1 or 2 casualties in 1st wave of the final stage, so I just gave up.