Is skipping spamton a major glitch?

Nope! Not by the rules for no major glitches, the only banned glitch in that category is door overflow

Warping straight to the Mansion from the Cyber Field saves more than 20 minutes, so it makes sense why it would be banned in NMG. Skipping Spamton in this city saves around a minute and a half, which isn't nearly as much as the former. Glitchless bans all skips and exploits including but not limited to wrong-warping. (though Toby specifically left it in for speedrunners)