I agree with their reasoning that engines are largely commoditized. Ours isn't, but (a) we don't iterate heavily on it any more (so just not hiring for it much in general) and (b) even if we were, most amateurs are using Unity/Unreal because generally there's very little reason for an amateur to write their own engine except for its own sake, so they wouldn't have the low-level experience of someone from e.g. the demoscene or with more general dev experience/credentials.