two reasons come to mind. One, as you suggest, is that less in the signal path is better. Two, base and treble controls really only work at one frequency each so they are not a very good adjustment. One assumes if you are the designer of a high end amp you tune it properly and tone controls just muck up the plan. You might recall graphic equalizers were popular years ago so you could really play around.
Kind of like asking for salt and pepper in a high end restaurant.
Kind of like asking for salt and pepper in a high end restaurant.