While you are of course entirely right, people do tend to vote based on the issues the head of the party is championing at the time so I'd argue that it's slightly more nuanced than just voting for the party given how the head of each party steers the policy in different directions
To be fair its not like the public even voted Sunak in, they voted Boris in and we then got the Tory's hand me downs (not that Boris was any better, granted)