Honestly that seems like Tamers biggest problem(s). He wants to turn an episodic show into a grand soap opera but he really doesn't know how to pace it out. The only comparable things would be the war against The Boys and WW3, but even then the lore wasn't that deep or that grand. People don't like Sonic Underground and want to beat their ass. The 'lore' was the forming of both The Boys and The New Boys. There wasn't big theatrics over how the universe would be put into peril or the world destroyed, or previous relationships weren't thrown into jeopardy over what happened before. It was straight to the point and easy to follow.
And then of course as you say the fanservice. The only fanservice SU fans really needed was Bartleby's huge muscles and Sonics fat ass. MLP meanwhile frontloads it, sometimes literally shoving horse ass in your face. I'm going to say that most of /mlp/-Tamers does not give a shit about the plot, and I can say that after lurking in their threads that they mostly just give a shit about seeing their characters appear like a set of jingling keys. The plot could've been about the stallions going to the Moon or eating Pizza Hut, the plot is irrelevant. All they want is horse ass. If Tamers uploaded a video of literally nothing but sexually suggestive horse ass his Patreon donations would go up tenfold. That's both the issues with nu-Tamers. It isn't made with the same 'tism that old Tamers had, it's just Tamers-themed softcore pornography with some thin veneer of plot to make it slightly complex.