No, you catch onto the gist. I have mentioned this before so let me say it again. Ambition is very much not allowed in the Democrat Party. Anyone who had it when this policy was enacted was left mostly safe, but even then many got purged. And any new members were vetted for a lack of ambition. The result is simple, there is a massive gap of leadership. Nobody to replace the current titans in the Democrat party.
The Republican style of leadership lends itself to the older members coming forward, but also makes an orderly line of succession. There are plenty who could rise to the task. But none for the Democrats, nobody is left as the old Guard dies, leaves, or enters irrelevancy.
This is why everything was on such a strict timetable, why Trump getting elected caused so many problems. Bills are due, and an increasingly short amount of time is left to pay them, and nobody will take up the torch once the current guard dies.