I'm objecting to the You will Eat This Do this because I Say So, school of parenting/child management.
Usually there are perfectly good reasons why children don't want to do things, or why they are being "defiant" on a particular matter.
If a child was in Reception, (a whole 2 years older) would you expect the teacher to put them outside the class for 40 minutes or stand against the wall, just because they were being defiant? That would be considered pretty draconian. Usually the child professional would come up with a better solution, and find out why the child didn't want to do something straightforward.
They will usually do what you want, if you pick your battles, reframe the problem, approach from a different angle. Just to insist they do something and stick to your guns ensures compliance but not cooperation or trust. Surely you want cooperation.
I remember one friend/acquaintance who was very hot on well behaved children who used to leave her 2 year old strapped in his highchair" until he ate his food". He didn't eat it, and she used to say, he is just so defiant. He went to school and continued to be defiant. By the time he was 10 she had completely changed her methods of dealing with him and got on much better with him
. He was her 4th child, (4 under 6) and I suspect she thought she had to run her house like a military operation. But in the end that just did not work with him.