Impact of Recommendation letters
I don't think that you have much to concern you. You can't get a letter from someone who won't write one, of course, but if your own advisor is on the faculty of such a university the assumption is that his/her word can be trusted. 

What you need is someone who knows you well and can speak honestly about your background and prospects for success. Your advisor is best placed to do that and support you. The superstars, if they could be convinced to write, would probably need to say things less directly applicable or useful to you. 

You need to put together a good case that you are well prepared and are likely to succeed. Your advisor's letter will help with that.