I have never understood this strategy. Just suppose that it's actually true, that Brigham messed things up that Joseph got correct. That still means that the LDS church is screwed up. Moreover, if this guy was really bad, doesn't that mess up the chain of authority? A weak link in a chain breaks the chain, it doesn't matter if it's the first, second, or 53rd link in the chain. And since LDS authority relies on an unbroken chain, this defense of Joseph by throwing Brigham under the bus seems to self-destruct.
But I don't think the defense actually works because Brigham didn't do anything worse than Joseph Smith, in fact in some ways he was marginally better.
- Both Brigham Young and Joseph Smith had identical views on the importance of polygamy. Joseph kept it secret and underground. Brigham made it public, which made the practice at least open and a bit more honest.
- Brigham is criticized for running a theocracy in Utah. However, Utah was just Nauvoo on a larger scale. While the council of 50 was kept alive throughout early Utah history, it never did anything as far as we can tell. Joseph seemed to have much bigger plans for secular rule through the council of 50.
- As far as I know, Brigham didn't marry other men's wives. Nor did he send men on missions in order to marry their wives in secret.
- Brigham ran church finances like it was his own personal savings and loan. But did Joseph really do anything different in Nauvoo? Brigham was simply better at it and had a good business sense while Joseph did not.
- Brigham never pretended to translate ancient Egyptian documents or any other documents for that matter.
- Brigham seemed much more willing to offer temple ordinances to all LDS members. For Joseph, you had to be part of the Quorum of the annointed.
- Brigham Young taught the kooky Adam-God doctrine. But the King Follet discourse had its own kooky ideas, those are just never mentioned.
The list goes on and on, but you get the picture. There is one event that is held up as proof that Brigham was worse than Joseph, the Mountain Meadows Massacre. Let's assume that Brigham gave direct orders for it to happen, so the blood is on his hands and Joseph never did anything like this himself. I'm not so sure, Joseph loved militaristic adventuring, such as Zion's camp and the Nauvoo legion. He styled himself "General Joseph" in Nauvoo. It's mostly just luck and happenstance that more bloody conflict did not come out of this stuff. In Missouri it did. The modern LDS church has invented a narrative where Missouri was nothing but evil Missourians hating Mormons, but Richard Bushman's biography makes it clear that there was plenty of blame on both sides. He also makes it clear that Joseph Smith most likely had a lot to do with the Danites. Plus, if Joseph does escape culpability for the events in Missouri, it's mainly because he went M.I.A. for this period of time, which sound to me like a bit or cowardice.
The bottom line is that the myth of the Brigham Young who was more evil than Joseph Smith, who screwed up the pristine LDS church is simply false. The evidence doesn't support the conclusion, and even if it did, it still doesn't help LDS apologetics.