The president can arguably pack the court and with his majorities nobody will stop him
If you believe the Supreme Court is an effective guardrail against tyranny then you're deeply mistaken. The only true safeguard against tyranny is the American people refusing to comply and responding with force of arms if pushed.
Assuming the US military remains loyal to the president... if you really think that the Proud Boys and their ilk, plus a bunch of random disorganized people with guns, have even the remotest chance of winning a war with the US military, well... I have a bridge I'd like to sell you.
And if the US military doesn't remain loyal to the president, then on top of a fascist dictator seizing power, then we'll have a military coup.
I don't care if you're a 3%er or a John Brown Gun Club fan, this is an absurd fantasy.