That's interesting observation Chris made.
I had VT-100 Mk 1 & 3 in the past, a friend let me borrowed his Mk 2 for a week. I have also had Sonic Frontiers Power 2, 3, 2SE and currently own the 2SE in addition to BAT VK-75SE among others. Side by side with BAT VK-75SE, VT-100 Mk 3 sounded rough, lack delicacy, slow, congested, etc. I could not believe my ears, neither can 3 other of my friends. Bass was not any better, it was such a disappointment I sold mine after a couple week.
However, SF Power 2SE (or even the plain Power 2) comes close to BAT! Bass weight is significantly better than BAT, but BAT is faster in bass, or faster overall. Top end extension, delicacy, air, refinement are all top notch like BAT, but BAT is still a touch better and expected given the higher price and lower output. I also owned BAT VK-150 (not SE) in the past, SF Power 2 definitely sounds better than VK-150 overall.
This is heard in the same system that includes SF Line 3SE and Sonus Faber Amati Homage, no other variable changed.
And like what Chris pointed out, SF Power series allow you to bias individual tube from top like a true reference grade tube amp. Only in ARC Reference series do they allow you to bias each tube. Reason is manufacture cost and VT series single resistor bias scheme is a very compromised design. For SF Power series, you only need to check bias once every few months, very little work involved.