analogluvr3
Other components - especially capacitors - have also improved with time.
Exactly. Tube design isn't exactly progressing further as the manufacturers would try to have you believe.That's not entirely true. For example, the KT-150 tube wasn't available when ARC released the D-79. Similarly, the 6H30 tube wasn't available when ARC introduced the SP-10 preamp.
Other components - especially capacitors - have also improved with time.