Testament always looked like they could be either gender they wanted to be at any given time so this us just the logical conclusion of being essentially a concept given form as concepts dont really have a gender in and of themselves.
Also ignore ResetEra their opinion on anything positive or negative is still going to be the same as holding a mic to a trashcan.

On the one hand, Testament is literally a manifestation of concepts beyond full human comprehension, so him being neutral instead makes sense from a lore perspective.

On the other, ReseterEra likes it.

So I'm torn.