Hmm, don't know. The author himself (ONE) had stated on one occasion that a fight between Boros and Garou in his perfect monster form (the one this thread is using) would be one hell of a battle.
That said, yeah, Garou's martial arts skill does give him an advantage in close combat, but Boros is also a skilled fighter (though no formal martial artist like Garou) and has energy blasts to attack from long range.
And wasn't Saitama only using one hand to do his consecutive normal punches against Boros only in the anime? Didn't he use both hands in the manga to do so?