With a properly designed output stage, I believe the input and driver tubes make more of a difference. I've been called a liar a cheat and a scoundrel, so save your breath. To me, the input tube sets the stage for what happens in the whole amp. Change output tubes and go "wow, I never heard that before". Change input tubes and say " Wow, my amp sounds completely different". Subtle but significantly different.
Output tubes are pretty much locked in by the O/P tranny and available voltage/current. The sound doesn't change that much, just the power available.