This is one of those "it depends" questions. It depends on when you are traveling and it depends on your personal definition of "difficult".
-First of all, if remembering to call right at the 7 month window is a lot of trouble to you, then it may be difficult. We see people on the Boards all the time that are upset they could not get their resort of choice. Then you realize they didn't call right at 7 months, it was more like 5 months or even 3.
- If having to get on a waitlist for part or all of your stay is a problem, then yes, for sometimes of the year it may be difficult. For some people a waitlist is no big deal. For others, they want to call, get the reservation done, and move on, without concerns over where they may stay.
- Finally "busy" times at
DVC do not always correspond to "busy" times at WDW in general. If you want to stay at BWV or BCV for the Food & Wine Fest (1st of October through mid-November), at VWL anytime during the Thanksgiving/Christmas holidays, or snag a Standard view at BWV anytime, or a Grand Villa at OKW almost anytime, it will be difficult. If you want Hilton Head in the summer months it will be difficult. If you want to stay anywhere but your home resort during Easter break, Christmas holidays, 4th of July or even the first 2 weeks of December, difficulty will vary from challenging (using waitlist or being flexible on resort) to impossible.
You can almost always get something at WDW somewhere at 7 months if you are flexible about location and occasional use of waitlist. If you generally want what you want, where and when you want it, you could find 7 month reservations difficult.