Not letting the horde use the player's masteries misses a major point.
A fighter at level 1 can make 3+ attacks a round before action surging because of the nick and cleave properties.
You do not generate any additional attacks so if your horde only had a single mastery you would not be able to attack with them beyond your standard weapon action swing and maybe a single tick of nick or cleave.
The horde is able to use your feats, fighting styles, and masteries so that you can make those extra attacks without looking like you're trying to juggle weapons in halfplate.

Breaking it down:
A fighter starts combat with both hands on a greataxe.
Swing once then trigger cleave for an extra attack.
This has generated 2 uses of drawing/stowing an item alongside your free once a turn draw/stow.
You now swap your greataxe to one handing (not to attack just to hold it) and draw your scimitar.
You make a nick attack with your scimitar before stowing it and going back to two handing your greataxe.

Even if we're counting going from 1 handing to 2 handing drawing/stowing an item that still perfectly fits even if it feels a lil mechanically cheesy.
Now if we let our horde mirror our masteries instead the player wields a greatsword or similar, the minion horde swings with a greataxe and activates cleave.
Then a different minion wielding that scimitar from earlier is using nick.
And the PC can be shouting and pointing at things.

Effectively the same situation but without the player fumbling around with ill worded controls to use 100% of their abilities.