In a 'normal' game where both junglers are split 50/50 between ganking and farming with one kill each, the solo lanes will reach level 6 while the junglers are still level 4.
Being two levels down **and** and at a level 6 disadvantage makes it impossible to gank. You'll just die in the process. Because you can't gank, you can't catch up, thanks to the jungle EXP changes. You're stuck farming your jungle while falling even further behind and hoping some misplay like a bad dive falls into your lap, until you finally hit 6 and bridge the ult gap. Except now the solo lanes are level 8, you're still pretty far behind, and god help you if the solo lanes decide they want to invade your jungle.
Basically, chain ganking from level 2 on is now the only way to keep up. If you're in a game where you can't gank (i.e. because all of your lanes are constantly hard pushing), you're completely out of luck, because farming your jungle isn't sufficient. You also don't just need a couple of successful ganks, you need **a lot** of them, since the EXP you get from pushing the wave after ganking is also further decreased by the pre-season changes.
This change was terrible and is just going to further push hyper aggressive junglers to the top of the meta, which in turn makes the role even less desirable than it already was. Nobody likes this. This really needs to be adjusted so that you aren't so far behind at all points of the game.
p.s. the gromp change is also a mess. Bottom side now has a major advantage, because they don't have to do krugs, which allows them to immediately invade top side after red. If the invasion is caught or doesn't work out, they can just retreat and still get 3 off of gromp + blue. This used to be extremely risky, because you would be stuck at level 2 after gromp + blue.