To veer away from the naval topic, other than in numbers, the Stuarts weren't underdogs in the Philippines in '42. My last day on active duty in '84, I met a guy who'd been a National Guard tanker there. He said that until they ran out of main gun ammunition, they went through the Japanese tankers like Schumer through a goose. He also said that he'd wished that they'd had AP-HE instead of AP.
I don't think the Japanese Type 97 Chi-Ha was anything like a PzKw Mk IIIb or IV, much less a Tiger, especially when the thickest armor was 26mm on the sides of the turret, so it's no surprise that the Stuart was effective in the Pacific.
The later versions of the Type 97 had a 46mm main gun which was of higher velocity than the 57mm, and made it more of a match for the M3, as it could hit at a longer distance and penetrate thicker armor.
The 37mm gun on the M3 had a MV of 2900 f/s and was effective at 1000 yards on 25mm armor, which was the thickest that the Japanese Type 97 had, so it had good performance against Japanese armor. It's performance against German armor was somewhat different, as evidenced at Kasserine Pass and Sicily. The Stuart continued good service in the Pacific, but was rather ineffective in the ETO, though it continued to be used there until the end of the war.
I would agree that the M3 going up against virtually any armor the Germans had was an underdog in a serious way, but they were on a much more even footing against the Japanese.