There is a lot to it beyond the airframe, in particular there must be qualified maintenance people. Further, 100 F-35s will require some form of upgrade to get to the latest software, so clearly having them "mission capable" isn't much of a priority right now.
Of those which are up to date, the MCR is, as you quote, in the "60 to 70 percentage range", which is in the neighborhood of many other aircraft in the list. What you failed to mention is that the squadron deployed to Kadena, Japan (an actual front-line unit) is running at a MCR of "above 70 percent" which is right in line with the best MCRs of the F-15s and F-16s. The F-16D (the most advanced) is running at a MCR of just 66%.
In short, what you posted completely supports the position that the F-35 is doing very well for such a new aircraft!
