It's not like RBT didn't put their full effort into designing the car. The truth is that Merc was the only team that went for Max downforce even at the expense of efficiency. Red Bull did the same thing they do EVERY season. They designed in as much DF as they could but only above a certain level of efficiency, same as everyone else. Merc just had the foresight to allow DF at a slightly dirtier level, allowing them to achieve more DF overall.
“To be able to actually make something is awfully nice”
Bruce McLaren on building his first McLaren racecars, 1970
“I've got to be careful what I say, but possibly to probably Juan would have had a bigger go”
Sir Frank Williams after the 2003 Canadian GP, where Ralf hesitated to pass brother M. Schumacher