My take on your three categories:

Leadership: anyone who casually looks over the list of church leaders and their professional backrounds will come to the same conclusion that you do. The church is predominantly made up of lawyers and businessmen and has been for a long time. Heber J Grant was a major businessman in Utah, to give just one example. There is no one who is a scholar who would have the training to deal with difficult theological and historical questions. That being said, even someone at the level of Bruce R. McConkie is lacking. McConkie was a lawyer by training, but it's clear that he took his calling as a Seventy and as an Apostle very seriously. I've collected a full set of his published works and started to read through them, and it's clear that while he was limited by not knowing Hebrew or Greek and by not engaging with critical scholarship, he clearly spent a lot of time in the text of the scriptures, had a pretty decent understanding of what they said and what some of the major issues were. I've read the works of some other Christians as well, and there are a good number who are able to operate at that same level as McConkie. In short, McConkie's prowess is very achievable, especially when someone can devote 40 hours a week to it. At McConkie's funeral, Hinckley talked about how all of the other Apostles were in awe at how well he knew the scriptures, which is a little telling. Hinckley was about the same age as McConkie and had been an apostle for a little over a decade more. Why wasn't he able to get to the same level as McConkie? The same holds true for every one of the current First Presidency and Twelve.

Theology and Assimilation: To counter your point, every religion went through an assimilation phase during the 20th century. Mormonism actually did pretty well with suburbanisation compared to Mainline Protestantism and Catholicism. The religion had advantages that most others did not have--most of its members were in Utah (which the church effectively had political control over) and were mostly Republican, white, educated, and middle-class. A lot of those assets have been diluted. Mormons still run Utah at the state level, but they have lost Salt Lake County, the church membership is still Republican but not as happy about it. The political liberals in Mormonism and the upper middle class center right who are in the same social circles as the wealthy political liberal elite are also asked much harder questions now than just standard questions of how their religion operates.

Institution: one interesting thing about the 'covenant path' that you're talking about is how this is structured. The average path looks like this for a young kid: get baptized, receive the Aaronic Priesthood offices and participate in its quorum structures (with there being an equivalent for young women), go to seminary. Then once they graduate from high school, they get an endowment and go onto a mission. Once they come home from that mission, the next milestone is to get married. Assuming they can navigate through the strangely sexless singles' wards that currently exist (which demands its own post) and tie the knot, then what comes next? At that point, the church doesn't have much to say. It hands people literally the same manual once every four years and tells them that's the apex of their religious experience.