Problem is, John McCain especially with a D next to his name is very electable. Maybe not if Obama is your opponent, but it's generally true.
The problem for the Dems with Kamala is that even though she has an extremely progressive voting record as Senator and comes off as progressive in the Biden admin years she's also going to get hammered to death for flip flopping for being the law and order California AG she was prior to going woke. She's trying to play both sides on the Israel issue which hurt Biden and Kamala is seen as anti Israel already. She's not seen as particularly smart or well spoken. She'll do alright with the resistlib base but seriously how many men are going to be enthused to turn out for her? Even black men under 50. White married women that do in fact have kids and aren't childless cat ladies can't stand her either. Suburban wine moms who have actually birthed children won't relate to her either. She'll certainly drive up turnout on the childless cat lady vote, but were they ever voting Republican anyway... ? Nope.