Ainsworth recalled that with his B- grade Viral Energy stat attribute, Solar Moon crystals weren't improving his strength that much anymore. Rather than being downright useless, the increase in the speed of his evolution became minimal let alone increasing it to B grade.
However, Ainsworth knew that it was normal for even Solar Moon crystals to become slightly irrelevant at a later stage. After all, he was already approaching the limit of this world's power level and from what he deduced, even Zombie Overlords and Evolver Overlords would likely appear much later.
Without his interference, Zombie Overlords would only appear within a year or half a year if his calculations were incorrect since the speed of zombie virus evolution was quite unpredictable.
His evolution speed was abnormal even by this world's standards as he was already at the rank of a Zombie Overlord/Evolver Overlord.