Final Cut Pro x lags way too much on my MBA.
Then again iMovie is pure **** compared to it.
MacBook Airs aren't really editing computers. That being said, FCPX worked decently on my 2011 11" MBA when I tried it out a while back, I only did it for fun though so I wasn't being too critical.
At the end of the day, FCPX was designed to blur the lines between professional (FCP7) and amateur (iMovie) applications, designed to cater to both people, if you don't believe it can be used in a professional environment then you're the one losing out; it's not your tools that define you but your skill. Caring too much about your tool is what's holding you back. Whatever gets the job done, use it, because otherwise you're gonna be spending more time faffing around trying to find the perfect application than actually getting up and doing something.