You’re right. I had forgotten that the Presidency, where we used to have a President who “presides,” has become an office held by an Emperor, who has to answer to nobody.
Good point.
The Executive has his own sphere of authority which is his to exercise at his discretion.
The checks on his authority are threefold: he can be cashiered for malfeasance through impeachment, his time in office is strictly limited, and he needs access to funds which only Congress can provide.
Exercising plenary executive authority makes him the executive, not an emperor.
An emperor, to resolve your confusion, has complete executive, legislative and judicial power.
The Constitution of the United States deliberately and by design gives the US President broad powers and discretion because the Framers - as discussed at great length in the Federalist - were fearful of legislative tyranny and tried to find ways to make the Presidency as strong as possible to forestall that danger.