Honestly not sure.
Game the thought with me... This issue with the Democratic convention is that less than 7% of the population watches it, and of those that so watch it 95+% were always gonna vote Dem anyway.
Does a rumor about a mystery guest (maybe it's Swift!) do more harm or good? If you drive more eyeballs that were not locks to vote Dem to see that speech last night from Kamala, well I can at least make a theoretical argument that that's a huge benefit. Sure, you risk disappointment, but nobody promised anything, and Kamala gets to define herself to a legion of voters would likely ignored the DNC and only really gotten exposure to Kamala via silly season political ads.
I'm not saying it was intentional. But I am saying I can make a case for it being a net positive, though.