That's not a problem unique to Mercedes. The commentator here actually said that you'd need about a 2 second advantage in regular lap times if you want to have some decent chance of overtaking on this course (and Hamilton had nowhere near close that, maybe half a second or even less as he had older tyres). Now I'm pretty sure that's quite the oversimplification (and it probably doesn't help that the top speed of the Ferrari was just as high as that of the Mercedes), but based on what I've seen in this race I've no reason to doubt it. Alonso slowing down everybody behind him quite a bit, and Verstappen was clearly faster than the Haas in front of him, but no way he could overtake, and when he tried really hard it didn't end up too well for him.
Speaking of Haas, while they weren't as fast as the top 3 teams, they appeared to be very strong. Not the best pit stops, though... At least they proved they are a partner team Ferrari can rely on
.