I can relate with Tallie. When boxing, if I spend any time trying to heal, my dps plummets hard. The healer merc coverage (even with a cleric in group) is indirect dps because it lets me maximize the damage I do from the dps characters I box. This is especially the case for someone boxing 2+ dps by hand. Tallie is just doing what works optimally for them, and it's very possible that having the cleric sit there doing little/nothing is optimal.