It does make sense to spend most of the time training on the ground since most fights go to the ground. Most fights do start from the feet though so you should spend some time training that as well in my opinion.

In our club, the beginner classes are all starting from knees. For the advanced classes, we start from our feet and I love it. That and the judo seminars we have once a month make the beginning of competition matches so much less stressful!