To out it VERY briefly, I think R’ Aharon and R’ Schwalb had different problems with TuM.
For R’ Aharon, the problem is MO in general, regardless of what particular MO philosophy one follows (TuM, TIDE, YCT, ect.). All are problematic as per the Chassam Sofer’s famous rallying cry of “Chadash Asur Min HaTorah – Anything New or Innovative is Prohibited by the Torah.” The Chassasm Sofer applied this maxim to combat Reform, but it has been extended to include any changes – even minor ones – from the way things were done in Eastern and Central Europe in the late 1700s and early 1800s.
For R’ Schwalb, I think, the problem is not with MO per se, but with TuM as a philosophy. TuM in many ways is inconsistent with the central tenets of TIDE. Whereas TIDE embraces “secular” knowledge, it considers such knowledge inherently valuable only to the extent that it is not inconsistent with Torah; it synthesizes Torah and rest of the real world, with Torah always controlling which aspects of the larger world are considered acceptable. TuM (as per R’ Solevetchick) on the other hand, rejects this idea of synthesis. In TuM philosophy, both Torah and Maadah are inherently valuable. While Torah is of course the more important and always must control our actions, non-Torah ideas (philosophic, artistic, political, scientific, ect.) are also inherently valuable and are also to be fully embraced. For TuM there is no synthesis – Torah and Maadah are at times at odds; Torah must control our conduct, but we can still be fully immersed in the Maadah world. That is what R’ Schwalb was taking about when he criticized having a Yeshiva on the first floor and studying apikursus on the third floor (for those who saw that quote in the other thread). R’ Schwalb was alos criticizing MO (TuM) rejection of the austritt principle, which is so central to TIDE.