That is not correct at all. The 4Runner has never been outperformed by the Gladiator in sales numbers.
Although Tacoma is now beginning to slump in sales now, despite a record sales year in 2021 (only beat by pre-1989 Pickup sales) like the 4Runner, it is a sales champion, NEVER toppled since 2005 when it became a leader and ditto for the 4Runner nowadays.
I'm not sure where that information even came from, as you are comparing only the March 2022 sales for each Toyota model against QUARTERLY sales of its American competition. At best the Gladiator sells only 6k a month against the Tacoma at more than 15k per month.
For my own unique reasons and also versatility purposes, I vastly prefer the Gladiator Rubicon 6MT I co-own over the 4Runner and my TRD Pro 6MT, but I wouldn't dare give it credit over Toyota in this arena. Even as a Ford Trucks professional out of Dearborn. I am that strongly objective.
Toyota sold an astounding 53,182 Tacomas and 34,907 4Runners in Q1 of 2022. Gladiator is something I always wanted for Jeep, just like many fans and objective observers since 2005 (concept) and the TJ Scrambler, but it isn't necessarily selling as impressively as it should be. Especially when the Wrangler sold 45,553 in the same period by comparison. The 4Runner isn't as hot as Wrangler, but it's also very old against the American flag's mascot vehicle...
The Tacoma and 4Runner at least have some parity, unlike the case where the Gladiator sells less than HALF of the Wrangler.
It's too far outpaced by its sibling, but then again I don't want to give too much of an opinion on this in here.