Question: There is this startup founded by well known people in the industry. 
They are making a very good product and I'll be proud to work on it, but my first motivation to apply is to be with (and to learn from) these great masters.

Should I tell them or keep it for me and focus on the product and the global company feeling?

Answer: 
"I've been very impressed with the work the founders have done in the past, and I'm excited to see what they're going to do next" is a good reason to work for a company.

"To be with these great masters" seems excessively sycophantic and toadying.
I am sure you can say that, but don't make it too dramatic. Include the performance of the company and mention you are excited to join such a successful company founded and run by the leaders. At the end of the day, we want to work with the best people and learn from them.