OP your statement is bullshit xD
Those gank spamming junglers, if they are viable it means they are successful, if they are successful it means their ganks are working and their victims dying.
If their victims are dying that means they are not farming or getting EXP, that means they cant be over the jungler killing them in levels, Simple logic x)
Just a few nights ago i had a Volibear jungle do exactly what you describe, spam ganks relentlessly as soon as he could, as a result the enemy toplane was below him in levels ....i think it was 3 by 17-20 minutes in.
Midlane? Down 2 levels and Botlane 3.
The only one in that game who had more EXP than the volibear there was our toplane who left his lane only twice and teleported back instantly right after......so yeah perhaps only junglers who can do this are truly good, but on the other hand i´d say they are OP.
And they who do this have always existed, and this style of relentlessly spamming ganks truly needs to be fucking gutted because it´s disgusting as all hell.
But Riot does not know how to actually accomplish that so they are taking shots in the proverbial dark and hitting basically everything except the target, kinda like how they are looking to "balance" Akali for instance.