The biggest difference is that those attacks haven't had any sort of real salience to date. Starmer doesn't excite anyone's passions, for better or ill, and it makes him really hard to demonize. The remarkable element of approval polling concerning him as a leader isn't that his approve numbers are really high (they aren't), it's that he's been the leader of a major party for more than two years, and in most polls the plurality opinion of him is "neither approval nor disapprove". The problem with Corbyn was that a lot of people (and not just consistent Conservative supporters) really just didn't like the guy, and so they were predisposed to believe negative articles about him. Starmer seems blandly competent, well-spoken without inviting controversy, and difficult to work up much hatred toward. will lead to
In some political climates, that would be seriously suboptimal. That sort of candidate doesn't tend to inspire any great wellspring of support. But this is very much a throw-the-bastards-out climate. Boris is disliked at a level that simply isn't untenable for a major party leader, especially the incumbent. And if he's turfed, the Tories don't have anyone in the wings who are particularly well-liked, either. "Yeah, but the other guy is worse!" worked against Corbyn; it won't work with Starmer. And if that's all the Tories have to work with after many years in power, they're going to lose.