5'10 is like the average height of an nfl corner.
What's most important for a CB is change of direction ability and being fluid at it. It falls under the agility generalization. Often times football heads refer to it as recovery speed. Usually with increased height and weight, agility decreases, reducing their coverage ability. It is more important for a corner to stay step for step with a receiver than being tall as him. In fact you prefer a smallish corner to be in a receivers facemask step for step rather than a corner that sizes up up a receiver but gives him cushion all day because he can't keep up.
Some physics to this? Momentum.
momentum equals mass times velocity.
ally defined as being hard to change direction. More momentum makes harder to change direction. I guess we are increasing mass in this case with bigger corners.
The other physics deal is moments of intertia. 2nd moment of intertia to be more specific. I guess in laymans terms... the longer the cornerback in his limbs... the harder it is to do work.
Therefore smallish corners have an easier time covering because of there change of direction ability, agility, recovery speed, lower momentum, closer 2nd moment of intertia.
5'10" seems to be the mean size of a corner that has that balance between coverage skill and height. So I wouldn't be worried about our guys.
I agree it'd be nice to have a bigger one though... but that's still a luxury.