Exactly how much power would an executor have over an estate?

No - an executor cannot behave like that.

Isn't it odd that the judicial system is set up so that if there is a problem with an executor you have to spend a big chunk of the inheritance to remove them. It appears its quite a common problem and the judicial system facilitates the executor, and you have to fight for your rights. Our Brother is the executor of our Mothers will and 3 years since her death, its still not in probate, he refuses to answer any questions, is rude and aggressive to anyone who asks a simple question, telling them not to bother him and get a solicitor. His country pub is surrounded by the farm the other siblings have inherited and he does not like the idea that there could be a change to his outlook, crazy I know, he says "over his dead body would anyone build on that land". Now we have to apply to the courts try to have him hopefully removed as executor, our Mothers solicitor protects him, as executor he has rights and ours are negated. It is a lousy system designed to breed corrupt thinking and enhance solicitors work. Anyone making a will please be very careful and appoint a truly impartial executor for your last wishes may or may not be carried out depending on the executor.