Growth has made it more difficult to book the
smaller DVC resorts (BCV, VWL & BCV) when you get to the 7 month mark. Growth has increased the number of members who are able to book the smaller resorts at 7 months, but it didn't (can't) increase the number of units available at the
smaller resorts.
Growth has only an indirect effect on booking your home resort if you call before the 7 month window opens. The indirect effect is that members who no longer can easily get into one of the smaller resorts at 7 months are buying add on contracts for the smaller resorts. They are very likely using the home resort booking advantage to a greater degree than the sellers of those contracts did. Nevertheless, prior to the 7 month window opening, you are only competing with other owners to book your home resort. Growth isn't a factor if you use your home resort booking advantage.
You are correct in that DVC membership growth equals growth in DVC units as well. However, it appears that the demand for DVC resorts is not equal. In general, VWL, BCV & BWV book up more quickly than the larger resorts, SSR & OKW. Until AKV is fully built, we really won't know for sure how quickly it will book to capacity compared to the others. In size, it is between BWV and OKW (IIRC).
And yes - when nothing is available, it is a popularity issue (or a matter of the late bird finds no worms).
DVC is a flexible system - it was not designed so that every member can stay during Christmas week. But there are enough unit nights available so that all of the points sold could be used to stay sometime within the year.
DVC works best for those who can plan ahead and those who either buy where they want to stay the most or are happy to stay at any DVC.