Wicked hasn't "stunt casted" since arguably 2006?
After Menzel and Chenoweth left there were a series of "stunt castings' of former TV stars (Ana Gasteyer as Elphaba, Rue McClanahan and Carol Kane as Madame Morrible) , former teen idols (Joey McIntyre as Fiyero, Jenna Leigh Green as Nessarose, and Randy Harrison as Boq) , and Broadway legends (Ben Vereen and George Hearn as The Wizard). This all appeared to stop in 2007, which if I had to guess was when Wicked's producers believed they had finally dug themselves out of The Producers Broderick and Lane problem, and was no longer in the shadow of Menzel and Chenoweth's iconic performances. This is compared to the current model of selling out a SRO show 6 months past the original leads contract without informing the buying public as Book of Mormon, Hamilton, and Dear Evan Hansen all did.
The only other instances of 'Stunt casting' in Wicked are possibly Carol Kane's second run as Madame Morrible in 2013, which could be seen more beneficial to Kane then Wicked as this was before Unbreakable Kimmy Schmitt made her relevant again. Then there is also possibly Justin Guarini and Ashley Parker Angel's stints as Fiyero, but neither performance was advertised as such. Wicked was Guarini's 4th broadway show in 4 years, and Parker Angel came to the Broadway production from the tour.
As such I wouldn't consider McCarten as 'stunt casting' .