I agree with your concerns about a monopoly, but just wanted to respond to your point about needing to “warm up”: Triplebyte gives you a free practice interview

I agree with your concerns about a monopoly, but just wanted to respond to your point about needing to “warm up”: Triplebyte gives you a free practice interview that doesn’t count (unless you ace it), and also lets you retry in a few months if you fail the actual interview.