From personal experience, I recently swapped from Dark Knight to Hero, and personally, I'm regretting my choice.
For reference, my DrK's weapons are Amaterasu's Final Wind (206 ATT, 30% boss, 9% ATT, 12% STR / Berserk Chain (21% ATT, All 6%) and my Hero's weapons are Sweetwater Two-Handed Sword (241 ATT, 35% boss, 10% ATT, 10% STR) and Virtues Medallion (50% boss).
When I was a DrK, I was hitting around 14-16mil lines with Dark Impale self buffed and I was hitting Hilla for around 13-14mil without hypers. I swapped over to Hero, and now I'm doing 8-9mil lines with Raging Blow and 11-12mil lines to Hilla with Enrage active.
Take into account that I did end up losing 20% ATT in the transition. But, to take this into a much more... objective discussion:
Hero was a nice breath of fresh air when coming to bosses. As a Dark Knight, you have to ensure your health is topped up and manage your Sacrifice uptime with hypers to maximize the amount of damage you can do in a time frame. As a Hero, it's as simple as toggling Enrage, popping Panic + Puncture and then wailing on the boss. Not to mention the added effect of Cry Valhalla which makes it so that you're unaffected by debuffs for the duration of your hyper, which makes their burst phase that much more reliable on bosses like Dojo Arkanium and Chaos Pierre (blue clown + red hat, pop hyper and sit in the corner wrecking him).
However, Dark Knights have unparalleled boss safety in the form of their life leech and Final Pact. It's always great to avoid death, especially when in later content, losing all of those buffs can seriously drop your damage significantly, so having that second life to fall back on (or third with Bishop's Door) makes them wonderfully safe. The problem is that debuffs really damage you, especially if you're forced out of Gungnir spam due to seduces, misses or locks.
Out of the two of them, Dark Knight does need more funding to shine due to their emphasis on Buff Duration, but they're also a safer bossing class thanks to Final Pact. Hero is an amazing bossing class but manages to be one of the worst mobbing classes in the entire game, making anything but bossing somewhat of a hassle. (Dark Knights at least have more range with Dark Impale and a far superior 170 vertical range hyper compared to Hero).