I don't know what the EU says about it, but Han generally carries a pistol in a low-slung holster designed for quick drawing; in the films he only ever shoots at virtually point blank range (a tad further against the probe droid but not much). This is not the design of a marksman but of a quick draw artist.
Whilst we barely see Boba shoot, he is at least using a longer-barrelled weapon with which you can make a case for marksmanship.
Still, Lucien's answer is probably best. If you feel he shoots like Clint Eastwood, then sure. I don't think it is contradicted.