Here is what I have seen. With the exception of a few really popular dates...early a December, New Years Eve, something is almost always available at WDW.
Here is the catch..it may not be the room size you want, it may not be for more than one night, or may require you multiple switches to get the number of days you want.
If you are flexible in travel times, and looking at 1 bedrooms, then you have a much better chance for sure. SSR, OKW, and AKV...due to size...are the ones that are more frequently available.
But, owning at HH will always lock you in to 7 month bookings. That means that If you ever did want to travel during fall or popular times, you won’t even be able to lock anything in. To me, that is the risky part and I would t buy a non WDW resort if the bulk of trips will be at WDW.