Congratulations, your post is probably the best description of what may have actually happened that I have seen, in years of looking for an answer.
It mostly blames Sessions, it lightly blames Trump, and describes a perfect storm.
However, the destruction to the country, and the pain it caused was immense. At some point, one of them should have recognized what was going on, and done something about it.
Sessions, being in the subservant role, should have fallen on his sword if necessary, as soon as the Strozk texts came to light. Instead, he dug in his heels, and argued with Trump publicly. He clung to his appointment that he had already tarnished irreparably.
Sessions failed, ultimately, and horribly. Trump survived, no thanks to Sessions, but the scars on his Presidency remain, and may never go away.
The difficulty for Sessions, Trump, and anyone in a senior political position during a crisis is that the demands on one's time, attention, and energy can be overwhelming. Many mistakes and oversights flow from that, with over-stressed, emotion-driven decisions all too common.