I would agree that he's not a naturally funny comic, (like maybe Billy Crystal or Jon Stewart) and he sometimes (much more over the past several years) oversteps into snide and now and then juvenile humor (making fun of names and people's looks.) I don't think though that your idea of him being "cynical, smarmy, or arrogant" are on the mark. Especially over the past few years there's been much to be critical about. His role is to be critical, but to evoke laughter and some relief from tension and tragedy. Of this former stuff he and all commentators in the media have been severely tested, comic or traditional, pundit or lampoonery.
I see him as a very smart, very literate and informed critic of the times using a bit of this and a bit of that in his comedy style, borrowing from every predecessor, from Steve Allen on. He is an amalgam of many comics and therefore tough to identify as a distinct personality.
So he is hard to categorize or to see as an individual "voice."
But make no mistake, he's not sinister, cynical, or mean-spirited. He's like the rest of us, who are trying to keep our spirits up, not let the would-be oligarchs, racists, and White Nationalists completely brainwash the nation.
Yeah, Mr. Colbert falls short of my idea of a really funny guy, but to call him mean nasty, and anything less than brilliant (have you noticed that all of his barbs and arrows are backed up with evidence and common sense?) would be to expose one's own shortcomings on seeing what's going on under and beyond what's being fed to us by the the actual cynical, smarmy phonies in government.