Here’s the TL;DR version of all of the above

The no-clamps slow throttle-up meant Starship stayed on the pad for a long time, throwing up concrete, rock, and sand all directions, damaging the pad, nearby facilities, and Starship itself.

By the time it left the pad, that debris had already destroyed three of Starship’s engines and likely damaged valves and systems that would lead to additional engine failures as well as an incorrect fuel mixture.

Starship was slow to reach every point in the flight plan, suggesting that other engines were not able to throttle up to compensate for the lost engines.

At what should have been stage separation, either software errors or more smashed hardware kept the main booster firing long after it should have shut down.

The result was an uncontrolled spin that required Starship to be destroyed.

...

But are two parts that were left out of Starship that absolutely doomed this flight and the decision not to include them falls right with the guy at the end of the first row at “Star Command.”

Those parts were not parts for the rocket. They were parts for the launch pad.

For some reason, Musk became convinced early on that he did not want the launch tower to have:

A flame-diverter or flame trench to redirect the blast from the booster’s engines
A water deluge system to dump a massive amount of water around the launch tower during liftoff

...

A flame diverter and a water deluge would have greatly reduced, or even eliminated, the damage to the area around the pad. They would have prevented the blow back of debris that damaged Starship before it even left the ground. It might have headed off the whole cascade of events that resulted in that button being pressed 4 minutes into the flight.

We don’t have to guess about whose decision it was not to implement these systems, because Musk already said he decided to skip these systems over the recommendations of his engineers. Musk even had a preview of what was going to happen, as past test flights of the upper stage also resulted in significant spalling of concrete structures and damage to at least one of the ships. He just made them try different kinds of concrete.