Then, again, what was Vettel doing into T3? He again had zero opportunity for a legitimate pass on his own team-mate. It was never going to work, I have no idea why he even placed his car there.

If I was Ferrari, e.g.; the team, I would have advised both of them to block both Mercedes into T1/T2 and fight it out later in the race when the race is normalised. I'm quite confident, Vettel would have easily won the race if he had gotten through the first lap in 2nd position. There would have been heaps of opportunity for the team to swap him on strategy or he could simply have gotten the win by driving better around the pit-window. But no, Vettel, for some reason thought he was racing for the win on the first 4 corners of the race.
The interesting psychology in this, is that perhaps once again, Kimi is racing for himself, if the rumours are true that Ferrari are bound to sign Leclerc for 2019.
In any case, even if the team did decide on using team-orders to get Vettel to win the race from a 1-2, it was never the best time to orchestrate a position swap on the first 400m with two Mercedes right behind you.