On the surface, a season with 3 races and the supposed 'underdog' team having won 2 of them you would assume the season is very competitive on the face of it.
But I'm not 100% sure the truth in that. We've kind of seen in past that when Mercedes have lost track position, they haven't always won. Races like say, Hungary 2015. And I'm not really sure if they're genuinely getting beaten on pace, or if circumstances have manipulated the results.
For instance, it seems to be that had Hamilton gone 0.010 faster in qualifying and got pole, converted that into the race lead, it would have been a very boring race for us as his pace was faster than the trailing cars. The problem for him was he lost track position to Vettel and then further got unlucky with the safety car removing the capacity for the undercut.
So overall, I'm not really sure the field right now is as competitive as it looks. I actually think come a 'normal' race, Merc could just cruise off into the distance.
I think Ferrari are at least competitive enough that mistakes Mercedes make actually matter, such that it may be the difference between them winning and losing.
Regarding the races so far this year, Hamilton pitted earlier than he needed to to prevent the undercut in Australia. But by doing so he trapped himself behind Verstappen. The reason he did this was because he felt the tyres going off and was unable to run away from Vettel. The gap was never more than 2s before he stopped, and had reduced dramatically by the time he went into the pits.
In the Chinese GP Hamilton was cruising. This is largely because the safety car negated Vettel's early stop for slicks. That and the fact the the Ferraris were bottled up behind the Red Bulls (OK Daniel) for several laps. So no clear picture could be seen there.
In Bahrain it was Vettel who pitted early to get the undercut. And it worked, despite the safety car. And because of some errors from Mercedes. Because of the situation of the race I think Vettel wasn't pushing very hard in the second half of the race, certainly not as hard as Hamilton.
You are right that in Bahrain if Hamilton qualified on pole he may have run away with the race. But that would also have depended on whether Bottas maintained 2nd place ahead of Vettel.