Yes... and no.
Jungle has the most influence on the game of nearly anyone. Where he chooses to gank and how well he does can make or break games. You can shut down that top lane Yasuo or Nasus by pitching a tent up there. You can bully a lane that would otherwise stomp early and let your own lane hold out until their late-game power spikes. You can snowball your team or attempt to sit on and prevent an enemy who is likely to snowball and you are the main person who is responsible for objectives... and objectives win games.
This however is a double-sided coin. The jungler can also snowball games against his team harder than almost anyone. I've seen more games decided by one team having a VERY good jungler than nearly any other role. A good jungler snowballs his entire team and takes every objective. A bad jungler snowballs the entire ENEMY team and loses them all. He can also just plain ignore objectives and lanes while the enemy jungler puts in work... leading to a game where the jungler hasn't died once but the enemy is still massively ahead because he didn't do anything to respond to the aggressive plays of the enemy. Jungle has the most impact on the entire team for good AND for ill.
Making it worse... the jungler has a hard time carrying bad teams. Even a good jungler can fail if his laners are bad... or he picks the wrong one to sink his effort into helping. It's like being a support in that you tend to lack gold and are VERY dependent on another person to succeed. In the support's case it's the adc, but the jungler needs to rely on his laners to follow up on ganks, help him if he's invaded or tries to rush an objective/get a pick in the jungle. A jungler with self-absorbed laners is going to HATE HIS LIFE, since he's isolated from his team but still VERY reliant on them for help. Tanky support junglers especially struggle if they people they are trying to get fed are just unable to do anything with the gold he gets them due to their own lack of skills or bad choices. In solo queue it's a crap shoot. Do you try to snowball your Riven top or is she awful and going to toss away the lead you give her on foolish tower dives? Do you camp bot to help out your vayne in the hopes that she can carry you come late, or gank for the early-game powerhouse who's gonna fall off if the game goes long? You have to make all these calls blind unless you know the players you're with, and you can never tell which is the right call.
That said... it can happen. Back in the ancient times when the game was fun... I played almost nothing but jungle and support all season and climbed outta bronze thanks to
and
. Stick with it and you can make it happen. Or just get a premade and get carried out like everyone else does. Boosting is legal now.