Just talking about the numbers - assuming their numbers are accurate, and going off your 4 hrs/week figure, I'd say that 7k images and 1 hour animation is good for 250 hours work. I'm not an artist/modeller/writer so I can't accurately predict how long 7k images would take to make. But I'd maybe triple it (~1000 hours) for all of the content described. That would seem a reasonable amount of effort per month for this big update.
Of course, I'd probably expect/want more than 250 hours work for a Patreon earning that much money. But if it is a large update (7k+ images), I can understand that it took over a year. I'm not a Patreon of any AVN's because of the inconsistency in any dev's schedule. If I can, I prefer to buy the game outright on itch/steam for the content they've already made, hoping they'll finish it or at least get a few updates.
If I was a dev, I'd want to do a release every few months, at least. Just to keep people interested. But I can understand that just doing a release is a fair amount of prep work. It requires notices on various platforms, upload, testing, and monitoring a release for bugs. If you get into a monthly release schedule, prep work can take up a relative large percentage of work done every month. So larger, singular releases can cut back on the release stress.