I suspect that Sessions's problem is that he doesn't have the management experience or skill to successfully manage dozens of high-priority matters simultaneously. Senators are not executives.
Session was attorney general of Alabama, so he has some administrative experience. However, he was only in that job for two years and it was obviously a less complex and demanding one than being the AG of the United States.
But your point is still valid. Most senators are just wind bags, not managers or executives. In fact, they have managers who work for them that manage their various offices and personnel matters.
Even if he were a great manager, he couldn’t do it all himself. And it must be difficult to know who he can trust.
Imagine being a CEO with 100s (maybe 1000s) of important projects you are responsible for. And imagine that 90% of your employees are actively trying to prevent your success. And imagine that you are not sure which 90%.