I’m a casual player time wise and honestly hate the idea of playing the meta or even knowing what the meta is. That’s not to say idk my rotation or not, but I’m not going to switch specs over it.
Is it worth it (would it be fun) to still try to get into mythics even if it’s just doing 0 and low keys? Not trying to play competitively just doing something harder than heroic, with better loot, that I can pug.
I don’t even see anyone posting m0 in lfg so I’d likely have to organize 
Youll find plenty of people doing low keys that only want meta specs because they wat hed videos on why they are good.
In reality, unless youre pushing +12 and over, your class and spec do not matter.
Play what you like and have fun
Definitely.
Just play what you want.
Meta chasing is an exercise in frustration.
As a casual player time wise myself, M+ is the only reason I play wow. I can hop on for 30 minutes and run a key and not commit to any schedule for raiding. It’s on my time. You don’t need to be a meta spec or class especially if you are just dipping your toes for fun. You can always post your own key and run with it. If you do run your own key and you +2 or +3 the level, I would suggest downgrading the key to keep the difficulty at your level to increase your chances of having fun instead of being in a run that you are not prepared for.
What about delves? You can do them solo, and lvl 8 bountiful delves give 610 gear, and doing lvl 8 delves also gives 616 from weekly vault. You don’t need to do lvl 8 right away, but I know many casuals who enjoy delves more than M+. Keys have been kind of awful to pug this season from what I’ve heard.
This.
M+ is more about patience and understanding how the system works. Playing something meta is a very small part of content up until keys that most of us won’t be running anyway.
You can absolutely suck at your spec but if you’re good at vetting/group building you can climb fairly well. So if you’re decent at an off-meta spec you can go about as far as the rest of us who aren’t exceptional gamers could hope to.
So, play whatever you think is fun. Anyone can get some content cleared if they play the game right.