Here's what I'd go by at this point (CAS = Close Air Support):
"But would an F-35 be survivable enough to withstand incoming small arms fire like an A-10 can? Given its range and the fidelity of its sensors and precision-guided, air-to-ground weapons, the F-35 may never need to be as close to its targets as the A-10. Moreover, the F-35’s sophisticated navigational prowess and impressive speed may mitigate any risk of incoming ground fire. But is the fighter jet’s coating, built with survivable composite materials, able to withstand small arms fire in the event that the aircraft needs to fly close to the ground? These questions have not yet been answered. Until they are, it is unclear whether the F-35 can truly supplant the mighty A-10. However, there is reason to believe that, given the opportunity, the F-35 fighter jet could be a great asset for the U.S. military’s CAS mission."
Given its range and the fidelity of its sensors and precision-guided, air-to-ground weapons, the F-35 may never need to be as close to its targets as the A-10.
nationalinterest.org
To stay on topic, there is also the question of numbers. The B-21 is smaller than the B-2 but is also cheaper. That helps with total number which also matters.