While I agree, I do feel that had McL carried on with Honda and it was another dog they would have looked so stupid? I think they had no choice, irrespective of Alonso, they just couldn't take the risk of a 4th bad season.It's still a Honda, which McLaren could not get to work properly over 3 years (you'd assume they would have had a reasonable amount of input into it) and blamed it for all of their problems.
They must have known something about its 2018 design to think that there was going to be no improvement, otherwise they would have stuck with it and seen the project through.
I also think that now Honda are making a PU that at least has reasonable power then they can progress quickly. Mind you with only 3 PU allowed I feel it won't be long before TR have lots of penalties. This should give Honda and Red Bull confidence in 2019 season, but I do feel that RB are only going to use Honda as a stop gap till the 2021 regs and they have their own Aston Martin badged PU.
As for McL's chassis I wonder if they mucked up the 2018 chassis or the previous ones were as bad but that was masked by the PU?