I havent used Mlem but Jerboa works decently well, and you can use the web version as a PWA.

I agree that theres alot of work that needs to be put into lemmy, especially regarding making discovering communities easier. they need to make it so when you click on a community thats outside your instance it automatically opens it via your instance, but other than that i havent really had many issues with lemmy.

you can find a list of a bunch of communities here https://browse.feddit.de/ , and if you wanna subscribe to them you search for them like this “!gaming@beehaw.org” at least that works on the web version, in the Jerboa app seems like you can just search normally and it should show up if its federated with your instance. It is still a bit buggy but thats gonna pass with time