Simpler take: The middle ground has been hollowed out. The old method (appeal to the centre) does not appear to be working. Starmer's throwing stunt policies at the wall to try to get some purchase.
It certainly is. And he'd maybe use more classy words for it, if he ever could be convinced to talk about his sincere beliefs. But as I said, I'm fully convinced that powerful people believe all the out there things that regular people believe. We've seen so many examples of it over the decades, and it's otherwise very hard to explain why Starmer would keep doing things which are neither a popular thing to do or the right thing to do.
The simpler take you propose doesn't work for me, because "throwing things at the wall" suggest unpredictability to me, and Starmer has been very predictable if you assume what I have been assuming for a few years now. His actions are not the actions of someone who would try anything, quite the opposite.
When the action is clearly going to hurt their political career, and there's no indication that it will put money in their pockets, and they don't even make much of an attempt to claim they're fighting for a principle, yet they clearly have a purpose in mind and keep doubling-down on it, you have to start looking for a motive somewhere else. "They hate their own people" comes to mind, but that's not really an answer because it still leaves you looking for the reason why they hate their own people. Not all leaders do, after all.