It was relayed to me by a mathematician doing the analysis on sizing a battery system at a solar plant in Hawaii. The trade off between decreases longevity with depth of discharge or increased up front costs for more batteries that don’t get discharged as deeply.

Yeah that seems too low to me, given that a lot of electric vehicles warranty their batteries for 8 years, and those batteries typically undergo more stress in terms of peak charge/discharge and such (and also would be expected to normally last beyond the warranty period - it’s not like they all drop dead after 8 years and one day).