Actually it is far better to minimize the number of launches to complete any mission.

Doubtful. To design a big rocket takes a lot of money - and big rocket doesn't get to be used as much as a smaller rocket sometimes, which makes it more expensive per flight.

The opinions of Elon Musk aren't always perfect either. Certain technical decisions are made not because they are best, but because they are available - like, SpaceX just knows how to do that, and considers it expensive to learn the alternatives. Which is quite justifiable on economical grounds.