I've never said you should hire people who can't tell var from const.

I've said that even if you hire people who do know the basics of the language, and some algorithms, and even could solve a toy problem on paper, you might still hire someone who can't code at scale. Coding interviews typically don't test design skills, documentation skills, ability to not get lost on a larger code base, debugging skills, tendency to avoid hacks and increase tech debt etc.

Those are different skill sets. Someone may know and know how to properly use var, let and const according to standards and current trends. They may understand it deeply. But that doesn't mean that they can explain it to you.

The question changes to: is what you are testing the actual skill you need? Are you hiring a teacher who is going to explain var,let,const as part of their job or are you hiring someone who needs to know how properly to use var,let,const?

Send me over any developer who fails your teaching requirements for var,let,const but has code samples with proper usage.

I've never seen a senior developer fired for poor coding. I've seen them get fired for being part of a department cut or because they got into a fight with the owner/boss. I've seen them fired because they make too much compared to outsourced resources.