i have absolutely no doubt that buttigieg did the most boring, banal crap imaginable when working for mckinsey, but he absolutely should disclose what it was. and warren should release her pre 2008 taxes. you run for the presidency, you gotta bare your rough ridin' soul to the country, that's the way it is (or should be, because obviously, trump).
i also disagree that it is a meaningless issue. i don't think bain capital is inherently evil either, but you'd be crazy to think it wasn't an electoral negative for romney in 2012. mckinsey would be for buttigieg as well, and even though he was a new hire and presumably had no power, what projects he worked on and what clients he worked for would be part of how much of a negative that would be.