That's all fine, but you shouldn't cheer your team when it starts with an own goal, claiming that this is just going to take a little more effort to win.
Hopefully, Biden won't manage to lose, but I am not sure that Kamala won't cost Bernie votes numbering far more than anything she might herself bring in, and I am not seeing why you'd expect something different. Biden's side won in the primaries - it doesn't mean that's an invitation to force the right wing down already not that enthusiastic about Biden voters.
I also don't think it's that different a ball game. Dem voters were called to vote only a few months ago, and sent Kamala to the deep end of the bench. Now she is back, by default, and the one who brought her back asks for those same votes.