I have not read Warren's op ed, but like Carson's Carnac the Magnificent, I can divine exactly what it contains.
Delaware is sort of an internal Cayman Islands in the United States. A tiny state, it uses lax, permissive laws on corporations and especially financial type corporations (insurance, banking) to attract these entities to operate from and enrich the state, to the detriment of everyone subject to those corporations operations.
And since those corporations "based" in Delaware are powerful entities any one representing that state will find themselves obligated to promote legislation in Washington increasing the power of the powerful over the powerless. It goes with the job. All politicians from Delaware will do this. And so too Biden.
A reasonable question is whether any politician from Delaware can plausibly serve as a progressive President as they will be have spent their entire political career backing corporate and financial power over the consumer and worker and thus be deeply compromised in that way.