VAC and others have built and sold monster tube amps with vertical designs but power is useless without reliability and user-serviceability.
Even the biggest VACs still use only 8 output tubes per side, compared to 16 in each Ref 750! At that point IMO you really need smart audio-bias circuitry to continually monitor & regulate the bias of each tube and shut down problem tubes (hopefully) before they spiral into a smoke show. VAC went that way starting with their "iQ" series. I have 200iQ and Master 300iQ now, and trust them implicitly. I believe ARC also started using their own version in Ref 160 series. But the Ref 750...yeah that’s gonna be a tough one to keep running. The fuses in my Rogue Apollos did NOTHING to prevent the KT90 arc/short problem.
I have also heard warnings about KT150 tubes. I would definitely move into KT120 or KT88. You need extremely reliable output tubes if you’re running 32 of them.