As such, the number of times a feature evolves means nothing at all for how diagnostic it is for particular clades. This one can be tested numerically. Have a look at the recent molecular systematics of birds volume edited by Mindell for a different view - a few nodes appear to be robust, but otherwise the relationships among living lineages are very poorly resolved. It actually looks like morphology may be more informative than molecular data for some of these groups, and even that has been minimally informative lately. Not at all, and I never said I would.
X is likly to evolve at some frequency.