The shield tank: takes all the damage, goes out of their way to protect the party and creates openings for party to attack.
The evasion tank: evades all damage, can't protect party cause of their glass defense, and can't make openings cause party too distracted with being targeted.
Stupid Hero Logic: I don't want this big guy tank with a shield anymore, he's getting in the way of my harem of girls, better fire him for something small and get a tank I want, like that evasion tank girl I saw a few days ago. Yeah, that'll work.
Result: "Hear ye, Hear ye, the Hero is dead!"