I think that the only content you can really outgear is the Lv.x0 content that lacks an ilvl sync, and that's because of the massive jump in max ilvl at Lv.x0. In general, Lv.x1-x9 content is implicitly ilvl synced by virtue of the character level sync. There's a reason why certain dungeons (Lv.41, Lv.65, Lv.71, etc.) are still called out as being a step up in difficulty: gear can only do so much for you.
Secondly, all of the MSQ was designed to be cleared by casuals on its release. Asking that everything have an ilvl sync down to, say, 20-30 over the minimum, or down to whatever happened to be the max on the content's release, isn't asking to pin them to some ridiculous level of difficulty. In fact, the Lv.79 and Lv.89 dungeons are already synced down to 30 ilvls over their minimum, so this is nothing that the game itself hasn't already shown itself willing to do.
Really, the major advantage of waiting to run the MSQ is not gear. It's the fact that the people you're randomly grouped with will likely have experience, and it's hard to understate how far knowledge and experience will get you and your party.