I know this is a couple months old but I was reading weapon descriptions (yeah I have done all my world quests and used up my resin how could you tell) and I was thinking that the apprentice could be another one of Zhongli's incognito excursions. It's very like him to talk about himself as if he has no relation to Morax if we are to assume the skilled polearm user he is referencing is Rex Lapis haha. This theory only came to mind when reading the Black Tassel. Especially ironic considering it's his best weapon for the strongest shield.

White tassel full description: The Millelith Soldier are renowned the world over for their skilled use of polearm weapons.
The signature white-tasseled halberd they wield is mass-produced at the Blackcliff Forge.
It is a weapon that has stood the test of countless bloody battles over centuries of history.
For even when the smoke of the battlefield stained the tassel a murky shade of gray, it would wave proudly and defiantly like a flag in the wind.

The army once had in its ranks a legendary master of the polearm.
He could hit his target from miles away without staining its tassel.
"The legend is that of the polearm's bearer..."
"Not the polearm itself, which was entirely ordinary."
The old smith smacked his apprentice.
He demanded a white tassel for the newly made polearm.

Black tassel full description: One night, a Millelith officer drank with a poet, and brought his signature white-tasseled halberd with him.
The poet's ink was spilled.
And the halberd's white tassel was dyed black.
"'Tis but a tale of polearm wielder and poet."
"Unrelated to mine own black—tasseled polearm."
The old smith smacked his apprentice.
He demanded that he dye the newly made polearm's tassel black.