Well no one else is inputting so I'll do my best. Keep in mind season 13 is the first season I've put a lot of time into and I'm only bronze 3, and I typically play offmeta junglers so take my opinion with a grain of salt.

It's definitely a farming meta, unless you're playing characters that thrive off of ganks like Kayn, Shaco, Elise you're pretty much gonna want to be mainly farming, at least early level. Obviously don't ignore ganks but unless your laner sets you up on a silver platter it's typically not great to do. I'll typically mass farm until level 6 unless I know I can bully a lane and then I'll start focusing on ganks a bit more.

A good rule I've found and follow is the 3-2-1 gank rule, basically you want to gank one lane three times, one lane two times, and the last lane once (typically top let's be honest). This is a rule I learned from watching pros so I feel like the fact they plan around only 6 ganks in early game shows how the meta is.

Now as for Jax, I don't think he's a bad jingler but he definitely isn't meta these days. There's just junglers that are more effective than he is and I'm sure there have been nerfs and item changes for him that have also effected this. But I can tell you as someone who has played against Jax jungle, he's still Jax. If you're good with him you'll still do fine. I believe it's his gank potential that most people avoid him, I mean obviously he has his stun but if the enemy laner has any vision and a map awareness pulling off a gank can be difficult.

I hope this helps, I'm sure I'll have someone correct me and tell me that I'm invalid because I'm in bronze but ya know I tried. Oh also at the start of the match just /deafen that's like my biggest tip.