They sent Ohtani and Darvish (the two best Japanese pitchers in the MLB), Sasaki (21 year old phenom who throws 102, almost threw 2 consecutive perfect games last season, 2.02 ERA/0.79 WHIP/12.0 Ks per 9), and Yamamoto (24 year old ace who won 2021 NBP MVP, 1.95 career ERA).
The US sent Lance Lynn (35 years old, 3.99 ERA last season, probably the 5th best US pitcher on his OWN team [behind Cease/Giolito/Clevinger/Kopech), Nick Martinez (32 years old, career 4.50 ERA, swingman who might not even win a rotation spot this season), Adam Wainwright (40 years old - actually ok having him on the roster for his leadership, but not as our #1 starter), and Merrill Kelly (34 years old, career 3.96 ERA, probably a #3 or 4 starter on most MLB teams that aren't the Dbacks).
The difference in quality is evident, at least on the starting pitching side. The US sent their old dogs to play while Japan sent their top players who are in their prime. The equivalent for the US would've been sending a rotation along the lines of Burnes/Cole/Fried/Gallen. Hopefully next WBC our top starters will be more inclined to play.