It looks like it's a battle for greater production legitimacy--between an undated MJ drawing and an actual, dated, Roddenberry-approved script.
Personally, I don't see any difference in legitimacy since neither of the two made it on screen as intended
. No dialogue explains the Enterprise as the 1st ship of the 17th design and the Space Seed scenes were cut.
It would've been definitive as far as TOS-continuity goes if the cut scenes made it into "Space Seed" though. Still, there is enough continuity bits to show that post-ST2, future in-universe historians would label both variations "Constitution-class" regardless of the "Enterprise class" label of TWOK and "Starship class" of the bridge sign. I don't have an issue with that and gives it a real-world flavor.