Of course, there are a variety of factors within the original Stereo 70 itself, and also with its interfacing to the rest of the system, that will affect the quality of the sound you hear. As I understand it, the Gillespie article is predicated upon an original Stereo 70 vetted for proper/peak operating condition interfaced with an appropriate preamp, i.e., a preamp with no DC offset at its output.
Dave Gillespie’s Stereo 70 that his test was based-upon was described as being in really nice condition. Regardless, any given sample of original Stereo 70 would have something like 35 to 55 year old parts inside. As such, sound-wise it might not compare well with a newer restatement of the Stereo 70 built with new and better parts. I suspect that in most cases when someone finds an original, even one that is functioning reasonably well, they will likely have to just appreciate it for the classic that it is. Bringing out the potential of the original design so it can compete with the modded versions is another matter.
I have owned original Stereo 70s that sound the way you describe. I also built a new Dynakitparts Stereo 70 not long ago and the difference is night and day. My newer Stereo 70 for the most part retains the original Dynaco circuit design but with some enhancements, such as a Triode USA 500uF cap board having low ESR electrolytics with polypropylene bypasses, Cree Z-Rec SiC Schottky diode for the bias supply, Dynakitparts independent biasing for each output tube for which I obtained four mil-spec pots, a few "boutique" parts here and there, and a few other things that I hope contribute to its quality. I think of these things as enhancements (not total changes to the circuit like the mods do) that level the playing field so a proper comparison can be made with other, present-day amps. The result? Really quite good. No complaints, in fact my wife and I feel the quality of its sound within its power output limitations compares very well to our Cary SLI-80 Signature, McIntosh MC275 Mk IV, and Parasound Halo gear.
IMO, the bottom line is that if someone is to take up Dave Gillespie’s suggestion to establish the sonic capabilities of the original design before making a decision to replace the circuit with a different design, then the playing field has to be level in order to make a valid comparison. I suggest implementing a one-to-one correspondence between the parts quality advantages available in modded versions and applying them to the original Stereo 70 design, i.e., again, low ESR electrolytics with polypropylene bypasses in the power supply, independent biasing for each power tube like some of the "mods" have, close tolerance metal film resistors, polypropylene coupling caps, larger power transformer, re-do all the solder joints with fresh solder, maybe new tube sockets, etc., etc… Yes, it ends up being its own rebuild project, but without going this route I don't see how a valid comparison can be made against the different modded designs that employ such improved parts vs. the old parts in an original.
So, if you suffer through a period of time listening to your terrible-sounding original as it is now and then switch to a different circuit like the VTA board with the accompanying new parts, then of course you will hear an improvement, but you still will not have heard what the original is capable of.