I think China (QF) is quite easily explained by bad-setup. Last year, the softest compound was the SS tire and even so, Hamilton only got pole with a 0.186 gap to Vettel in 2nd. Arguably, it was extremely close there too, yet on a tire that was harder than what Pirelli supplied this year, going with the US.
So even if colder conditions and harder tires is something that typically benefited Mercedes last year, it wasn't that visible last year too at this track. The 4 tenths Ferrari had in hand over Mercedes in qualifying are down to insufficiently getting the most out of the tires. That's my guess anyway. Yesterday during the race, Mercedes was very competitive with Ferrari - probably as quick, not slower. We saw this nicely in the first stint when Vettel was leading Bottas and drove out a small gap, yet that compromised his pace later in the stint when Bottas/Mercedes made the undercut work. In the 2nd stint, Bottas was quick enough to get a small gap to Vettel and it was only the blockage by Kimi that lead to a period of laps where Vettel had DRS on Bottas but couldn't make a move stick. The rest of the race is simply down to strategy. Overall, I think Mercedes and Ferrari were pretty much equal during the race - especially once the Mercedes was on the soft and medium tire (vs. US during qualifying).
The last 3 races were brutal by Mercedes. They should have easily won Melbourne on sheer pace alone - the car was evidently a beast. But this advantage was also exaggerated somewhat due to the fuel saving Ferrari needed to do - they purposely set-up their car for less downforce and less drag to be more fuel efficient and compromised their cornering speed somewhat. This is why in Melbourne, Ferrari were extremely fast on the straights but lost out in the corners. Bahrain was a toss up, advantage to Ferrari for qualifying but pretty nigh on equal during the race, perhaps with a small advantage to Mercedes/Bottas, but perhaps this was also exaggerated due to the offset in strategies (Mercedes luring Ferrari into a compromised 1-stop strategy).
We will see how things continue. Baku was a strong track for Mercedes last year. Mercedes/Hamilton need a strong showing. It being a street circuit, we may see something akin to Melbourne this year. Maybe.