That's not exactly how it works. PRD is generally implemented so that the first proc chance is actually lower than the desired average value.
http://dota2.gamepedia.com/Pseudo-random_distribution
Furthermore, there are still elements of pure randomness, such as bash, evasion, Ogre Magi's Multicast mechanic, Faceless Void's Backtrack, etc.
Hard to compare two games completely different. But game mechanism are clearly under control in Dota2 (don't know for LoL but suppose also). Element of randomness can all be countered by items and heroes capacities are derived from items themselves. In Coh2, there are no items giving you immunity from damage for a period of time.
But anyway, I'm not against RNG, but here it takes to much space on the gameplay design, those mechanisms are lacking of control limits.
when a units has 50% chance to pen another, it can be over 10 shots, 5 first pen or 5 first bounced, and honestly at any level of skill it gives the same result. For sure, at higher level a player will manage the situation better, but the result is the same at the end, your windows opportunity has been annihilated, not by your opponent but pure luck/bad luck. I don't see that in Dota2, from the 1200 hours I have played that game so far, I have never experienced this feeling of being so unlucky, same when I took a super multi strikes from Ogremagi...