The point clearly stands that had Reform not been a thing, 2024 would have been a conservative landslide.
What we got was a Labour landslide, what we should have got was some coalition.
It's certainly not a given that all the 2024 Reform vote would have gone to the Conservatives: a good chunk of it would have likely been disgusted abstention, another chunk to other anti-system parties (mostly of the right fringe, I suspect, but not excluding the Greens despite wild ideological differences), and likely a further (if smaller) chunk to other parties which were simply not the Conservatives (including Labour and the Lib Dems).
Edit: the best analysis on this is likely to be in the latest volume of the long-standing The British General Election of XXXX series, which has just been published online[0]. I haven't had time to look at it yet, though.