I think you're really misreading Biden's campaign. It hasn't been brash or chest thumping or provocative. It's been rhetorically normal but with a candidate that routinely gets confused and misspeaks and is also somewhat thin-skinned. And there's no way he out-Trumps Trump and, even if he did, it would likely serve to hemorrhage more support than it gained by making him look like a fool to voters who don't value foolishness (Democrat voters).
For all wai's flaws, I think he got electability against Trump completely right. Buttigieg would be strongest, followed by Sanders, followed by Warren, followed by Biden. With Harris being the weakest.