Toro Rosso have just done a 1:18:363 on the hypersoft aswell, only 1.2s short of Vettels time this morning - half a second quicker than the hypersoft time from Vandoorne this morning.
Have they dumped Honda at the worst time or was the PU not that bad all along and the problem McLaren's?
I think it's a bit of both to be honest. I think Maclaren had a lot of requirements that put Honda into a corner (size zero) at a time when Honda needed to figure out how to build that type of engine. It's telling that both Honda and Toro Rosso have talked about how they had to give each other space and freedom to get on with their respective jobs.
The PDFs linked upstream from Reddit show how subsequent changes to the Honda engines all seemed to come with some kind of significant weak spot. Maybe Honda have sorted that out now, especially as TR has given them more cooling and more space.
There's an interesting note in there that Maclaren knews that the size zero packaging would bring problems with cooling and put power down, but the size zero concept was supposed to overcome that with the aerodynamic gains from such a small and tightly packaged engine - but those gains never materialised.