20% isn't minor. It will be the difference between being able to mine profitably or not.
There is a physical limit to how fast hardware can mine. Hardware which is allowed to skip repeating part of the hashing process will be able to mine faster and cheaper than hardware that cannot. Eventually the faster hardware will be profitable and the slower hardware will be uneconomical to run.
Bitcoin was designed to allow anyone to be able to mine it. A mining environment where one entity is able to mine 20% faster than all the others because they are using government power to cripple the competition doesn't work out well for Bitcoin as a whole.
You dont count the fact the 20% faster units should have higher initial cost price to pay the patent rights. How much more the initial cost should be? To get most revenue for the patenter it should be very close to the +20% expected lifetime profit of the unit. In other words, in ideal world the expected lifetime profit for normal and +20% faster patented unit should be the same eventually.