There are decent (free and paid) third-party clients that make Reddit a much nicer experience on mobile. On Android I was a big fan of Sync for Reddit, and on iOS I've been using Apollo.
Every once in a while I'll open up the official client and I'm just blown away at how bad it is. It's constantly trying to get me to watch livestreams of people doing random things unrelated to my interests. Why would I ever want to watch a livestream on reddit?
It is honestly impressive how bad Reddit's mobile app, and main websites are. Its just so horrendous and so slow and so confusing, and so bad. If you go to a post, its hard to see comments, and if you click in white space it redirects you somewhere almost at random. It takes forever to load anything.
When a million apps are better in every way and the old site is better, its confusing what they are doing over at reddit.
Apollo is attractive, but being closed source and giving all permissions to a social media account makes me a little nervous. It seems relatively time-tested, but even if the developer is benevolent it increases attack surface area.
Seconding the recommendation for Apollo. It's definitely a shock to get used to at first, but it's so customizable that it reminds me a lot of RES if there was a mobile app version of it.
+1 for Sync for Reddit. An amazing app. I've tried to use the official client for compatibility reasons, but the difference in UX is just night and day.
Unless you click on a Reddit link while inside of old.reddit.com; it will then take you to that page, but show you the default 'modern' theme. Same content, just 10x slower.
I wrote a Greasemonkey script for force old reddit and rewrite links to point to old reddit except in some edge cases, since gallery links don't work on old reddit at all (they 404).
old.reddit.com + reddit enhancement suite is a fair superior experience. If they kill that off they are toast and I think they know it. It will be a repeat of the Digg fiasco.