When I used to keep track 3500 miles was common for a chain. i do reasonably well with chain maintenance.
Cassettes last a lot longer if you don't ride with a worn out chain. I have worn cassettes to the point where a new chain skipped, but only once. Think that was before I owned a chain stretch gauge. I almost certainly own cassettes that are older than many of the members on this site.
For some people chain maintenance is a religion, almost like they lose sleep worrying about a chain not being optimal. The latest obsession seems to be waxing chains. Do yourself a favor and avoid chain lube arguments.