Thinning can be a disaster unless the stylist is extremely skilled. Razoring curly hair is also really risky, because it tends to encourage the ends to split. I feel bad for your poor hair!
Very thick, curly hair sometimes can benefit from special techniques like the carve/slice method from Ouidad, in which the curls are cut to fit into each other, or the tunnel cut method from Jonathan Torch, in which some curls are cut out entirely from underneath. Not just any stylist can do these cuts.
For most curlies, cutting long layers (meaning not much distance between the longest and shortest layer) helps reduce bulk and avoid the "triangle-head look."