Mclaren didn't realise their car was awful, as well as the engine, when they swapped to the Renault engine they found that out. They had also insisted Honda make the engine really small, size zero packaging or something, but when the Honda was swapped to Red Bull they eased the requirement so that years engine was better, plus RB have a very good car.The thing about F1 I don't understand is how McLaren reunited with Honda failed with these new engine regulations.
The red bull managed to suffer a bad engine and still have albeit limited success but McLaren just drop to nowhere.