maybe yes. max's support for 'sophisticated' envelopes is not the best, i'd say.
when the max5 skd came out, i was playing around with the new functions for bezier curves to write a gui external that does curvie envelopes. but when i wanted to do it right, implementing attribute support and making it pattr aware etc, i got bored and left it half working half crashing...
you could of course record [curve~]'s output into a buffer and do all sorts of playback/loooping stuff.
or maybe have a look at [techno~]. help patch comes with a jsui-based curve editor. kind of awkward to control, though.