Most people whom have expressed this sentiment to me have generally not been exposed to much more than the defaults.

Reddit with defaults or r/all is a horrible experience. It is what you make of it though, and if you don't make anything of it then it is obviously not for you. The advice I always give to someone trying reddit is to 1. make an account 2. unsubscribe from all of the defaults and 3. search it for whatever interests you. Pretty much everyone can find something for them, and moderation is going to be variable which I think is actually a net positive. A well moderated sub is a gem, such as AskHistorians, but not every sub needs to be moderated to the same extent as AskHistorians to remain useful or relevant either.

Anything hobby specific generally has decent enough modding but the value of those depends on the quality of the community specific to the hobby, so for example I subscribe to a few Nintendo-related and Game-related subs. AskHistorians is generally always good. Changemyview is generally enjoyable but each thread can be hit or miss depending on the OP. I like listentothis for finding music, OldMaps, MapPorn and InfrastructurePorn are nice to look at. Neutralnews was pretty decent when I last looked at it but I don't use reddit for news anymore, and DepthHub is one of the few general purpose subs that generally always has something interesting.

As a rule, the more general purpose the sub is, the lower the quality of the community, especially if it has lax moderation. I'm not someone that is into gifs or "memes" so you'll have to ask someone else about those. I don't use reddit or any one site for news because I don't need that in my life, I have other channels for anything that actually matters. Programming subs are usually pretty good resources for whatever tool, language or technology they're promoting that you use or are interested in, but I steer clear from the pointless debates.

I would say search a few of your hobbies, whatever they are, there's probably a decent model train collecting sub but I wouldn't know, and if you want to use it professionally, search it for whatever tools you use. There's self-development subs like getdisciplined and most subs have others you can look for in the sidebar if you really want to dig down the rabbit hole, but go in prepared to unsubscribe from all of the defaults and build up your own personal collection of subscriptions from there.