I definitely agree with your last paragraph here. Try to vote in progressives in every primary we have access to in order to use voting to make a difference, yes.

However,

the donors want to win

You mean they want everything for themselves by buying politicians, right? Because often times Dem strategy is so incredibly tone deaf the only thing that’s clear about it is that they aren’t trying to win an election, they’re simply doing what the donors tell them to do. In this case, it’s the classic pretend fight, send strongly worded letters, and then let the republicans narrowly pass the massive tax break for the rich. Which is in fact a win for the donors, but nobody else.