Not saying Merc are relaxing, just that they have more to lose, if their development has taken a wrong turn. Short of a catastrophe they have this years championship, so why risk it.
They only have something to lose if you think a team could make changes test and implement enough in the remaining races to catch up and pass Mercedes.
It depends on how aggressively Merc wants to go after future years championships. I mean, with the advantage they have this year, there's no way known Merc should be able to lose - although they seem to be doing everything possible to screw things up via their driver management
