plainly, free our feeds are grifting.
the relay at this point is non-archival and can be spun up trivially. with a small sliding history window for subscriber catchup u can use like 32gb of scratch disk space and keep a few hours, the relay is literally just a subscribeRepos forwarder from PDSes.
the AppView is vastly more expensive to run since you need to handle the write volume of all bsky activity. if you build a non-bsky app on atproto this is a non-issue
the issue here really is that nobody writes about the state of things in long form outside the network so it's not really known how fast things move and change by those not engaged with the platform
Re: the relay, that depends on your needs. My impression from these sorts of "run a relay on an RPi" projects is that they're only dealing with a subset of the full firehose Bluesky's relay has to deal with - be it a shorter timeline (as you mention) or only concerning themselves with specific accounts (like the relay operator's own "following" feed, in the case of someone running a personal relay) or what have you. Pretty sure even Bluesky's relay doesn't try to drink from the whole firehose (or if it does, it's tolerant of "dribbling" so to speak; I recall a Bluesky dev blog post about how temporarily dropping posts from users' feeds is acceptable if the relay can't keep up).
Re: write traffic, my understanding is that the appviews shift most (if not all) of that burden to the PDSes, no?