Level 20 Oneshot Magic Items

[ciarannihill]

So my group finished our first campaign last night (level 1-9 homebrew thing), and though we may come back to the characters and setting in the future we're planning on running Dragon Heist starting in 2 weeks (to give them time to prep new characters and kind of decompress from this campaign), in the week interim we're going to be playing a level 20 one-shot I designed which is a sort of... Inter-planar game of capture the flag combined with war. The players have been conscripted into the conflict soon after entering a higher plane and are able to outfit themselves with implements magically copied from the Prime Material for the duration of the conflict.

I'm deciding how I should allow magic items to be distributed for this one-shot, I'm not overly worried about allowing them to break stuff since it's level 20, but I don't necessarily want them dual wielding Blackrazor and Axe of the Dwarvish Lords, so I'm considering implementing a point-buy system for magical equipment for this game and I'm looking for input on it:

15 points:
Artifact = 15 Points
Legendary = 12 Points
Very Rare = 7 Points
Rare = 5 Points
Uncommon = 3 Points

Any thoughts on the point system? Need I be more lenient or more harsh? Is this kind of too much work to bother with? I'd love some feedback.

EDIT: In case it matters they're going to be playing a Stout Halfling Zealot Barbarian 20, a Wizard 19/Cleric 1 focused on battlefield control magic and an Assassin Rogue 17/Fiend Tome Warlock 3.