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Looking at Data the "Average game length" hasn't really changed drastically, around 20ish seconds.
On average, High Elo games still end in 25-ish minutes
And low elo games still 30-ish.
If snowballing was significantly reduced, i'm guessing we'd see a perceptible increase in "Game length"? But that doesn't look to be the caseNvm, Phreak just stated otherwise, and he has the full picture, so he's likely correct.
Changing average game time by 20 seconds is significant movement.
Also the feel of the game is more important than the length of the game. Late game means more than early game already: Kills leave you dead for longer and they're more likely to lead to a Baron, Inhibitor, or another valuable objective.
Of course if it goes too far, it makes the game feel like nothing matters until 20 minutes. Some amount of the game must snowball to be fair.
Anyways, this is all to say snowballing appears to be substantially down without a huge increase in game time, which are both pretty desirable outcomes.