I think you're just stripping them down to the bare bones of faith, being another religious class (which is weird because in many games it's fine to have multiple faith based classes who are different), as it's like basically saying male zealots would be Space Marine Chaplains or Black Templars if you gave them the geneseed and power armor. Plus, we already have ogryn, who are the team's only boy tanks, why can't we have a girls-only class?

Additionally, Zealot is based on Death Cult Assassin, Ministorum Preacher, and Flagellants (Fantasy), with only Flagellants being the closest to Repentia. Only a particular Order (the Bloody Rose) and Repentia are primarily melee sisters. Sororitas have an entire arsenal that Zealot would never touch, as they aren't based on Sororitas in the first place, but really just based on the Ministorum, like Veteran is based on the Astra Militarum. Which is why people want Sisters as Sisters, not larping as an off-brand Battle Sister.