Maybe my original comment wasn't clear, but it was directly referring to Sanders' criticism of Buttigieg during the primary, which is that he had "50 billionaire donors" and that Sanders had zero. That is referencing individual donations, not PAC or Super PAC coordination. I did not mention some of the Warren campaign's criticisms -- e.g. that a Buttigieg advisor openly signaled strategy on Twitter (likely to VoteVets) -- that actually had some meat to them.
If you dislike bad faith arguments, then I'd imagine you wouldn't be a fan of simply barking out words like "billionaires" or "donor class" in order to rile up emotional reactions and conflate actual campaign financing issues (like what you've reference) with non-issues.