500k outdoor in the winter is also not the same as in spring or summer. I have 400 done, all indoor, in 12h45. I don’t look for flat routes. I look for nice routes within events with some social interaction. I could not do 12h on Tempus Fugit or that kind of routes.
Outdoor is harder, no doubt about. But I don’t ride outside anymore in cold or rain. And like someone said…2h for 8 days on a trainer is also not that evident.