No, they can't "win the damage race" when they want, though that wasn't his claim. Unless it's an AoE situation. Look at all those games from campaign 2 again - Caleb is only the top damage dealer in 15 of 141 episodes, generally when there is a, you guessed it, AoE opportunity. His two biggest spikes by far are in episode 86, when he managed to hit a fireball into a cluster of cultists (this one game is almost 10% of his damage for the entire campaign, largely due to this moment) and in episode 116, where he hits a home-brew AoE spell, "Widogast's Web of Fire" into 4 objects that didn't have saving throws.
Campaign 2 hardly had "cracked magical items," to the contrary, in response to campaign 1, Mercer greatly reduced the availability and power of magic items. At level 17 Yasha has only 18 strength and a "scaldsabre" (basically, a flametongue). For most of the campaign she wields a +1 weapon and has 16 strength.
Hussar's claim is very specific: with regards to overall damage dealt, it was that "I'll bet you dollars to donuts that your casters are number 1. Every time." That is demonstrably untrue, and in my experience is not even close to being true, as critrolestats.com supports. To the contrary, a caster being the number 1 damage dealer is very much the exception, and almost always, as I originally asserted, in situations where there are plenty of targets and the caster has good AoE spells.
Casters are usually not the primary damage dealers. Martial classes are. Which is fine, casters have plentiful other roles to play. All I'm saying is that focusing on damage, like casters have it made in every aspect of the game, is not supported by the facts. If you want to argue that casters have much more flexibility, you'll get no argument from me.
