If most of the people here think politicians should be deciding who to investigate then you might be right.
Most people on this site support the US Constitution.
The Constitution makes the president the Chief Executive, who is responsible for executive functions. The DOJ, which performs executive functions, answers to the Chief Executive. The Chief Executive answers to the voters and in cases of impeachment, the Chief Executive answers to Congress who in turn answers to the voters.
So you would change all that and the Constitution and make the executive functions in the DOJ unaccountable to anybody?