The thing is, with all the nerfs first to camp respawn timers then to camp xp (as well as the skuttle changes which massively favored champs that can skirmish earlygame), Jg has become more like a "2nd support" than it has been the whole time since i started playing in season 6.
Right now as JG you biggest window to be impactful is from levels 3-9 (earlygame) by spam ganking lanes and getting them ahead, midgame because of your reduced xp/gold your impact falls off fairly hard and your role is mainly objectives like rift/dragon and sometimes 3manning people with your team. Late game at this point you are so far behind solo laners in xp and gold and ADC in gold that you are basically a smitebot with a small degree of teamfight impact.
I played Jg the most in season 7, and IMO outside of the ardent meta at the end of s7 (worlds) s7 was the healthiest most balanced season I played in LOL. If you were even you might be 1-2 lvls behind the solo-laners, if you were behind probably 2-3 lvls behind, BUT because respawn timers were better you actually had options, now even if you're ahead your probably still 2 levels down on the solo laners, getting invaded, and your camps have slow respawn timers so your way to get back into the game is purely through capitalizing on an enemy mistake.
One big issue is these JG nerfs made the "better jg difference" WAY more impactful, past seasons the less skilled jungler had more options if he was getting beaten in the jungle matchup, now the game is so snowbally that if for example pre-12min the enemy jg has 2-3 succesful ganks and you have none, you are basically super behind at this point and UNLESS your laners make an active effort to collapse and basically baby you, you have no way back into the game.