"Lightsaber" is a good description of the glaive
Here's the Tier 1 Khuzait Nomad (whopping 20 Polearm Skill) armed with all glaives
Here's 100 Nomads (with the Glaive) against 100 Legionaries; they lose but inflict pretty heavy casualties (this is 1 vs 1, T1 vs T5 mind you)
Now here's 200 glaive armed Nomads against 100 Legionaries
Sorry, the Glaive is a broken weapon.
Doesn't matter what unit you give it to, how low their armor is, how low their skill is with it -
it will still dominate in all melee. Actually the Billhook is a bit silly too, but it has shorter range and does less damage as I recall, so it's not as infamous.
Until the Glaive's mechanical crazyness is sorted out, giving it to ANY unit, Khan's Guard or otherwise, is just gonna create balance problems. To be fair most swinging two handed weapons are pretty strong, but that's usually balanced by the fact it's carried by FOOT shock troops with no shield.
I mean it get it, it'd be nice if the very Mongol inspired Khuzait could carry a weapon they historically used. But as is in this game, it's just out of control. And I'm pretty sure the Glaive is not why the Mongol Empire was as successful as it was, even if it was a pretty good melee weapon.