First of all, it's obvious that the Tories aren't "guaranteed" to win in 2024, although of course there's plenty of time for them to improve (or to avoid worsening) their position before the next GE. Also, the +9 Labour lead would certainly be enough to ensure that they are the largest party, so that in itself means that the Tories are at a significant disadvantage in the current climate.
Secondly, just on tactical voting, it is extremely difficult to measure this for certain (and, even to the extent that you *can* measure it, a voter who tries to vote tactically might still get things wrong). Still, the evidence seems to be that even when there are coordinated campaigns to get tactical voting going, the impact is relatively minor in practice, as most people simply don't (or, as I say, vote tactically but "wrongly"). See, eg,
https://journals.sagepub.com/doi/full/10.1177/14789299211027423 ,
https://www.tandfonline.com/doi/abs/10.1080/13689880500505231 -- in general the consensus seems to be that about 10% of votes, or less, in any given election are cast tactically. The point is that most people don't engage with elections that deeply: many, of course, don't vote at all, and many of those who do just go in to vote the same way they always would regardless of the campaign. Approximately 30% of Tory Labour voters in 2019, for example, had "always known" how they'd end up voting: see
https://lordashcroftpolls.com/2019/12/how-britain-voted-and-why-my-2019-general-election-post-vote-poll/ ; I have a note of scepticism that the large number of voters who apparently only made up their minds in the last few weeks, or on polling day itself, is entirely accurate, but never mind.
Thirdly, I think the +9 lead here has to be put into proper context: there are no London/Scotland figures, for example, and this is also based on a projected national share for the LibDems of around 20%. That, and the similar overperformance of the Green party, probably serves to benefit Labour in a GE: people vote for the LibDems/Greens because it's the locals and it doesn't "matter" so much, but many of those could be expected to return to the main opposition party in a GE. That probably gives Labour a larger lead, assuming nothing else changes.
Still, the GE is a long way away. Time for things to change. But the fact is that, right now, the Tories are in a seriously bad position.