imagine if the onion service decided to be the malicious exit node itself. It’s not (Exit node) but could it travel back through its relays (possibly even skip) to the rendezvous point that track you via traffic correlation size? Would the rendezvous point and the two relays you have all have to log or would 2 (entry and rp) be enough?
Yes, HS can track you in exactly the same way, but using a bit different technique: both of them do inject a clearnet-breaking code or link to be pulled by your browser or software. So they will give you a hook token and will listen for a clearnet IP that will provide it during a query. Traffic correlations and/or route tracing are too expensive and laborious to be used widely, but this tactics is as cheap as hell