Removing CDR will make most mages not viable.
Removing crit chance would make ADCs non existant.
Most assassins wouldn't give a fuck about either of these, Zed's job is done after he blows his entire combo on a spuishy, Talon's job is done once he unleashes his entire combo, LB's job is done when she blows up one person. Katarina and Akali already has resets in her kit.
In fact assassins like Talon and Kat would get a buff since either their ultimate is on a fairly low cd when compared to most other ultimates in the game. Katarina can even reset her ult.
As for cooldowns, LB Q is on a 6 second cooldown at all ranks, her W is at 10 second cooldown at rank 5 (and W is usually maxed on LB to eliminate her problem with csing). Her E cd is 8 sec at rank 5. Her ult cd is 24 at rank 3. Now apply the 20% CDR you said yourself she will have and you see that if she doesn't use ult to burn Banshee (why would she do that anyway?) she can easily do her combo 6 seconds later