The thing is that, due to the very nature of the design choices that go into champions and the general game in LoL, the game itself is VERY vulnerable to snowballing if riot doesnt make tweaks like this. Heroes tend to gravitate around the same power level and have similar power curves through the game, at least much more similar then other games of the genre. Heroes have power spikes at certain points and when certain items get completed, yes, but i've never seen anything like the good old days of AD stacked twitch doing 900 damage with crits at max attack speed.
DotA, however, isn't that vulnerable to snowballing because the heroes are all very impactful. So what the enemy phantom assassin is murdering everything in two seconds? If you team has a lion/lina you can probably just burst her down with an ult+dagon combo or chained CC (hard CC is a lot more prevalent and more powerful in DotA). Maybe you have a winter wyvern that can basically use her ult to turn the enemy team onto their own carry and give 100% physical protection to someone, or you have a doom with aghs, which can basically shut down every active and passive skill with a single button for nearly half a minute while doing damage over time.
What I'm trying to say is that, with proper coordination and the right item choices, even an underfed team can shut down a super fed carry in dota, while this is generally harder to pull off in LoL, so riot needs to tweak the game to specifically not favor snowballing, or else people who are really good with a certain carry will almost always snowball out of control. This is essentialy why every pro LoL player recommends that people pick a snowbally hero and learn him REALLY well, while in DotA you need to be able to properly play at least a group of heroes, since they're so impactful that some heroes can almost shut off others. Counterpicks and bans are a lot more important in dota overall.
Hell, dota has heroes based entirely around the concept of snowballing yourself AND your team (hello, bounty hunter), and matches don't tend to be very one sided even then, unless your team screws up massively, of course.