You should check out the film again, his spins were clunky af, it's quite obvious his stick is just some plastic prop not at all suitable for combat imo.
It's easy to stay in an army where you've been your whole life, what's hard is to give up on everything you knew because innocent people were killed.
Tr-8r is a little bitch who sold his soul for decent wages and a good breakfast every day, while Finn leapt into the great unknown because he felt that was the right thing to do. That's real courage.