P.S.
The M-18 entered service in the Summer of 1944: in other words, when the ETO had less than a year left of war.
The bulk of the worst fighting - except for the Bulge - took place before that, with other tanks and tank destroyers. The US also had air superiority by then, with zero-length 5” HVAR fighters, making the need for other anti-armor less extreme.
I also did not mention the Pershing: same scenario.
And yet some of the worst fighting was at the Bulge, where the M18 ripped the hell out of opposition armor for little loss to their own. Also worth remembering that the M18 (as the T70) fought at the Anzio breakout and came ashore in Normandy at D-Day, though not in the first waves.
Considering that the M18 was there from day one of the major part of American fighting on the ground in Europe and drove all the way to the Elbe... kind of hard to say it wasn’t there for the bulk of the fighting.