The biggest limitations to RSS is are discoverability and adoption.
For all the awful shit that the algorithm does, it also sometimes suggests other things I might like (note: this small benefit does not outweigh the price)
The other thing holding RSS back is that not enough creators actually use it.
In terms of use, you can easily use RSS for any YouTube channel (at least with invidious) (peertube also works and odysee as well). Also there is a lot of journals using RSS and fediverse also uses a lot RSS (thankfully, I use it all the time)
You can get a pretty good estimate by watching download stats. Some people will download but not watch but for the most part it is one download per listen.
Large aggregators typically send headers that hint at how many subscribers they are fetching on behalf of. Although it would be nice to standardize this.
Nice to know, a dedicated scrobbler would still be nice. For the podcasts it is important for negotiations with advertisers. It's always good ti "prove" something