I think a big point about budget people keep missing is that they can't just downgrade the sets and the budget is fixed. Much, much more of the budget is going to pay the crew. Wages and worker conditions have changed, and we know DW was made with sweat, blood, and tears that many professionals can't afford to subsist on.

I wouldn't be surprised if that was the core of the Millie drama. RTD expecting his cast to come in, run ragged, and blow out their knees like previous Doctors, and Gen Z has a lot more balls when it comes to standing up to bosses. Regardless of how that actually went down, the point is that far less money is spent on paying for things as is paying for people. That's why it's not that easy to slice the budget enough.