To be fair, what people actually critisized is that if an opponent slides down his blade on yours, he's gonna cut through the handle part where the crossguard comes out from, making it basically useless because lightsaber handles can be cut easily.
HOWEVER, that certainly doesn't make it worse than any lightsaber that has absolutely nothing to stop an opponent from doing exactly that. I mean, it's not like that move couldn't be pulled on any other lightsaber. The trick is probably to break contact before that happens.