The problem was that his job title was Supreme Allied Commander. Not Commander Allied Land Forces, which he effectively appointed himself as after 12th Army Group was stood up. It was Eisenhower's poor decision-making in the latter role that Monty had a problem with.
Said poor decision making being essentially 'But he gave Patton some supplies too'.
Both Monty and Patton were right in that, if they were correctly supported (ie got *all* the supplies), their army could have won the war.
But Ike was absolutely correct that the Germans only chance to win the war would be to try and counter-attack the flank of any unsupported single army driving into Germany.
Therefore, a broad front attack so as to not give them the opportunity.
And then when that counterattack finally came at the Bulge, Ike, Monty and Patton roflstomped it together - with both Patton and Monty refusing to wait for orders before doing the right thing of redirecting reserves to counter-attack.