Yes, it is sensible to reduce the number of commissioners, because the number that there are now makes it hard to get anything done. There are so many people involved now that it is very costly, and it also feels a lot like the United Nations. Reducing the number of commissioners makes it easier to be effective.
One thing plaguing the European Union is the size of its bureaucracy. Reducing the number of commissioners from one per country to 2/3 per country makes sense to reduce the bureaucracy and let decision making happen more expediently. When member states have trouble agreeing with each other, hopefully fewer commissioners will reduce the time it takes to get things done.