It's no secret that ADCs seem to be doing a lot more damage than they should earlier on in the game. The coveted two-item power spike of Infinity Edge and Stattik Shiv seems to make ADCs a bit too strong. While you can of course argue that the problem lies in either the crit system or the auto attack system as a whole, I personally think that the problem lies in Shiv's ability to crit. Currently Shiv does a bonus 60-160 damage, but with an Infinity Edge crit, that jumps up to 150-400 bonus damage (assuming I can do math). On top of that, Shiv does magic damage, which is a different damage type than most ADCs, making it difficult to itemize against early in the game. So, my theory is, if you lower the potential burst of ADCs, they will seem like sustained damage dealers and not like assassins with zero counterplay.
As a side note, the design behind Shiv is for it to be an item for wave clear. So, I would be ok if it could crit minions, Hell, I think that Shiv ALWAYS critting minions and NEVER critting champions would fulfill this fantasy well. It feels really bad to hit a minion wave and leave all the minions alive because you didn't crit.
Of course, these are just my two cents. Feel free to point out any flaws in my idea, but please try to keep the ADC hate relevant to the conversation!