Having 20% slow debuff is very nice, because it scale versus the enemies very well, whereas the weak DoT attack just doesn't scale versus tougher opponents. I would lean towards picking up 4 skills in defense tree to get the slow debuff, can see it being very handy in helping you versus FATE bosses and such when there's few around. If you think about it, a boss being slowed = less damage taken = choco's heal/regen is more effective and/or used less often (more time for it to dps).

7 in the healing tree is a must, the 30% healing buff is very good.

As to the attack's having an Internal CD, I don't think so, because I've seen many times, back to back usage of the same WS, in a short period of time. Whereas, other times, the bird goes for a long duration between WS spam.. its too random.