really off-balance ER11A collet nut

I'm new to DIY CNC and I'm trying to build my own simple grbl-controlled CNC engraver. I built one leadscrew axis from parts, which works well. I got an assembled ballscrew axis "RATTMMOTOR EBX1605 200mm / 7.87" CNC Linear Stage Actuator" which also works well. I got a spindle motor "Genmitsu GS-775M 20000RPM 775 CNC Spindle Motor" from Amazon which runs smoothly up to full speed at 24V, or at least just the motor part of it does, with nothing attached.
When the provided ER11A collet nut is attached to the spindle shaft, it vibrates alarmingly when run up to speed. Removing that nut from the shaft and looking inside, I see what looks like an unfinished machining job with an internal step that is quite visibly off-center, I would say at least by 1 mm. At the advertised speed of this motor (20k RPM) that amount of off-balance mass is obviously a bad thing. I don't know if I'm just unlucky, but I'd say this will never work as designed. Is there a known-good source of accurate ER11A collet nuts? The spindle shaft it is threaded on to is 14mm in diameter.

 

In case new users are allowed to post photos, here is a look at the inside of the problem ER11A nut.
I do have a mini-lathe and I later managed to significantly improve it by removing most of the off-center material with a boring bar, but the motor still has more vibration at higher speeds than the bare shaft without the nut attached. I see Amazon also has some ER11A nuts sold separately, but looking at the user reviews I see some complaints apparently about the same issue I've got.

 

For what it's worth, I just got a "Luo ke ER11 Spring Collet Nut Set - AAA Level High Precision 1/8 Inch Collet Chuck for CNC Engraving" and this nut looks much better visually, and does not shake when run through the full speed range, like the first one that came with the Genmitsu brand spindle one did.

 

Initially I did, and found it out of balance. Then I tried removing the tool and the collet and tried running the spindle with just the nut. I'm presuming the collet by itself is balanced, because there's no way to register it on the shaft, so it could be at any rotational angle relative to the spindle. So the nut must also be balanced by itself if the whole unit is to be balanced, and all the evidence shows to me that it is not.
Since posting this, I have seen it claimed that the off-center machined ring is intentional, to allow the collet to be more easily inserted and removed from the nut, and some such nuts have a balancing divot drilled on the outside of the nut, so it becomes more-or-less balanced overall, such as this item: Amazon.com "All nuts have dynamic balance holes, which can prevent wear and noise."
That's the same company that provided me with the nut on my spindle motor that had this problem. My nut had no such "dynamic balance hole" so I guess I still have some questions.