Actually it is far better to minimize the number of launches to complete any mission. For example, Elon Musk has repeatedly mentioned that he is not currently a fan of in-orbit assembly. So having a really powerful engine is of great utility. The problem is one of cost-benefit. Having a huge engine means a big rocket which needs to be launched multiple times to achieve economy. But there are not too many missions around which require such capacity. Just look at the proposed SLS cadence. So having a Falcon Heavy with 27 engines is a much better solution any way. I cant wait when Merlin 1Ds are replaced with Raptors on first stage on Falcon Heavy. That would be one monster of a rocket.
> 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.
