If 2/3/2 is impossible or impractical, let’s do Main and Off tank queues.
Make 3 more new heroes of each type of tank to diversify the pools and we’re there. Ripped grunts in power armour, waifus in bikini armor. Maybe a frickin’ squirrel piloting a cyborg. Boom. Tank queue will be mobbed. No need to balance main tank stacking.