Without old Reddit (and third-party apps on mobile) I'd stop using Reddit completely, I have zero doubts about that.
Reddit subscription is $60 a year. That removes ads.
old.reddit is showing the same issues that i.reddit had, such as redirecting you to "regular" reddit if you click on a title instead of the comments. I think old.reddit will keep accumulating small papercuts like these until enough users give up, at which point it will be shut down without recourse. Reddit can't do this right now because some moderation features don't work well outside of old.reddit, but the fact that everything outside the "official" website is being degraded or shut down should give you pause.
Old reddit has been working exactly the same for quite a few years now and I can't remember it ever redirecting me to the new version. Perhaps this happens if you're logged in and have the new version set as default or something?
It was recently killed, just like old.reddit.com will be.