Agreed, the MMR balancing problem has been a major game-breaking issue for too long now. Both instances of low MMR antags or low MMR raiders getting free wins due to the massive imbalance that negatively affects the higher MMR side are well documented in the forums, and talked about constantly.
I remember pre-Hades, or even for a while after Hades, that these balance issues did not exist, or were rarely seen. If I antagged a game, I knew the mobs would be weaker than normal, but it wasn't nearly to the degree they are now with a large MMR difference, and it was consistent. But now unless you are within like 5% of each other, the mobs are either all unstoppable juggernauts that will 1-shot the raiders, or they are little more than paper targets and ammo pouches to be picked up.
That said, the bandwagon argument that skins and guns are ruining the game is getting old. Doldren's skin/gun were created months ago, by a team that likely has nothing to do with balance programming, since they make art assets, not programming. You can see them both in the screenshot here on the website showing the Aneska battle, that was put out 5 months ago. Same for Hive's skin, which also showed up around that time. And Mikah's. It took 5 months between Ginebra's slave skin in January, to Iune's Vaasi skin in June.
But it's popular to blame the art team because the game balance got screwed up in a patch some time ago :| Constantly updated games like this and Warframe and others know that they have to not just put out balance patches and bug fixes, but still must put out new content, new things to play with, or players get bored us playing with the same skins, same guns, same characters, all the time. I recommend watching the Warframe documentary and Rebecca talks about these exact complaints.