It's been said many times that random elements in a competitive game aren't good for gameplay. Critical hits, Dodge, Sion's passive, Phage procs etc.
They're not really fun to fight against ether, someone crits you 3 times in a row from only a Cloak of Agility it's certainly a wow moment for the person, but a OMG BS! moment for you.
Anyway there is a possible fix I'd like to say in just a short point.
Say if having a 100% Crit chance let you crit every hit (which it does).
Having a 50% crit chance would crit every other hit (so: Normal attack, Crit, Normal attack, Crit etc.).
It would delete the randomness of it while still keeping the effects identical. Not only that but would be a lot more reassuring that you deserved to die to a crit, it was their predetermined time to crit you.
33% crit chance would cause every third attack to be a crit (Normal attack, Normal attack, Crit, Normal attack, Normal attack, crit, etc..)
A 66% crit chance would go: Normal attack, Crit, Crit, Normal attack, Crit, Crit, etc.
Having a number less divisable by 100 chance of a crit would average out over 100 strikes ( having a 28% crit chance would give you exactly 28 crits every 100 attacks, spaced out evenly).
Meanwhile Phage/Trinity procs would be every 4 attacks the slow happens.
Sion's passive reduces damage 40 times every 100 attacks he's hit with, spaced out evenly.