It seems more like a gameplay nuisance and leads to annoying moments way too frequently. If everything just ignored unit collision, wouldn't it just take away a lot of negatives? What are the positive aspects of unit collision as a mechanic (im genuinely curious).
Maybe consider removing unit collision for everything but champions, dragon, and baron?
Edit: An intriguing Riot post, answering a few of the important questions. But I've started to steer this thread in a more argumentative direction: Although there are cases to be made for the positives of champion-minion collision, does that outweigh the negatives? Share your thoughts
This isn't something I've thought about deeply, but what thoughts I have had resulted in these conclusions:
Minion collision is one of those seemingly subtle game play elements which you rarely notice (except when it causes you to fail spectacularly), but which exerts a dramatic effect on how the game works. If all champions were ghosted, lane aggression would be dramatically easier and less risky, leading to more snowballing. The tutorial's exhortation to "Stand behind your minions!" protects you not just from skillshots, but from the enemy making a beeline for you as well. It also limits clicking difficulties (i.e, deny) and minimizes visual confusion (especially for newer players).
Champion on champion unit collision exists to make unit selection possible using just the mouse. If the ranged AD could always hide under the tank, the game would more or less degenerate into body blocking as the primary means of peel/carry defense (absent something like tab targeting). This sort of gameplay strikes me as cool when it is the exception (Teemo hiding under max stack Chogath), but not the rule (Kogmaw hiding under Taric all game).
I have posted on the subject or the "stuck on minions" bug before. We are well aware of the issue and are trying to resolve it. It's a really tricky bug to track down the cause of, let alone resolve. Last I heard, we had tentatively connected it to a discrepancy between the unit collision radius assumed by the pathing system and the actual one in game.