6 team in domestic cricket is way too low, similarly having 37 teams are over the top. looking at Indian domestic teams, if they managed to get their act together then they could even build at least 3 world class teams but not sure if its going to happen in our lifetime.
How many is ideal, in your opinion?
I have followed the Sheffield Shield competition in Australia for the past many years. I would say without a doubt that it is the best domestic first-class competition in the world right now. I would rate it above the county championship of England and Ranji Trophy of India. But in Sheffield Shield, they have only 6 teams.
Even in the West Indies, they have only six first-class teams. Until the 1990s, the Busta Cup was regarded as one of the best first class competitions in the world. Similarly, the Plunket Shield competition of New Zealand also features only 6 teams.
India was having around 27 teams, before a supreme court judgement forced the BCCI to add 10 more.
As you can see, out of the six countries with a proper first-class setup, 4 are having just 6 first class teams each. Exceptions are England and India. England still maintains the quality, because each of these county sides are running for more than 100 years. The same can't be said about India.
The other six test nations (including SL, Pakistan, Bangladesh.etc) don't have a proper FC setup.