On face value, it certainly looks as if things are getting a bit strained within Mercedes, and having two other teams biting at its heels is definitely exposing the team's weaknesses.
Over the first three years of its dominance, in reality all that was really required was make sure that Lewis Hamilton and Nico Rosberg didn't knock seven shades out of each other too often. If Mercedes could manage that, which it did most of the time, then big points were always on offer and championships followed.
In 2017, things started to get a little tough. Valtteri Bottas replaced Rosberg and Ferrari started to become a big threat. If Mercedes tripped up, there was a Prancing Horse waiting to trample on it. So instead of just battling an internal pressure, there was an external rival.