Yeah, my situation is very similar to yours - not much interaction from many of my patrons, but a decent size back catalog. For my patrons, I don’t think many of them would care about accessing my old stuff, and those who did could easily find it on YouTube or contact me to request it. (My main patreon benefits involve early access to new content and behind-the-scenes stuff like rough drafts and works in progress.)
I am running my BMC in parallel with Patreon. Also working on building subscriptions directly into my website (hosted by Bandzoogle). It’s a bit of extra work duplicating my posts, but I feel that it may be worth it. I’m more focused on giving potential new patrons a choice than migrating existing ones anywhere (which I agree is unlikely). I might encourage my patrons to check it out though. I’ve already had one existing patron donate via BMC, and they’re not extremely tech savvy. One of the main complaints I have from patrons is that Patreon seems designed by and for tech-savvy people, which my patrons mostly are not. That is the main reason I am looking for other options - I want to make it easier for people to support me. Sadly Patreon seems to be getting less usable for both me and my patrons as time goes by. My experience in this thread was the stimulus for me to start seriously looking at other options.