Better off 50 2h/31 Slash then you are 44 2h/37 Slash.
I think having a higher damage floor is much more important than having a higher damage ceiling for consistency, especially since your max damage isn't terribly impressive - especially especially at low RR.
Going thrust or crush loses a decent amount of auto training points.
That's not how AT works on Phoenix. Crush is a viable option since slowest crush 2h is 5.7 or 5.8, I just personally think 6.0 Apoc is very worth it. Thrust would be completely viable but lvl 51 2h thrust weapon selection is terrible.
46 or 48 chants is personal preference, as 28 AF with a 62.5% uptime isn't gamebreaking, but can be nice for melee train burst on a squishy.
So you sacrifice the best AF buff in the game for 3 points of slash that's still only lvl 31? You should really be keeping AF buff as the last chant in your line anyway, DA is mediocre.