It makes sense to talk about “RSS aggregators”. Especially it makes sense to talk about “RSS aggregators that speak a specific vocabulary on top of RSS, host 99% of content using that vocabulary, and if you host your own RSS feed with said vocabulary they’ll show it in their aggregator but can ban it any minute”.

Did I just describe Apple Podcasts? Huh. Regardless, yeah, there’s no “ATProto instances” technically, but there are ATProto apps and the single biggest one now owns the trademark to the protocol name.