thank you for your feedback. I can confirm everything you are saying. And to add to the above comment it’s worse than you think. using many other usb adapters I have encountered this problem. it is not just symptomatic of gl-inet but also ocurrs with clean openwrt 18.06 and 19.07.x and furthermore when I thought I had found one that would work and would always set the usb adapter to radio2 on a soft reboot. I was smiling and overjoyed only to discover a power cylcle throws it elsewhere into the line up at radio0 or radio1.
but, alas I found the tp-link wn722N version1 always stayed at radio2 because of the other atheros drivers being similar but not exact. 
It also supports 802.11w
another solution you could use is luci-app-travelmate. this may interfere with other gl functionality but no more than how your using it. like your alfa interface that you created, it creates a trm_wwan interface where all wisp radio connections exit too. this has some very useful feature sets. (advanced or daring users only)
when using it you do have to disable gl_health and not have any access points on the adapter you use for wisp
directions here.AR750s Keeps disconnecting - #32 by wellnw
Myself I only use travelmate with clean openwrt
this adapter works great in many wifi routers from gl… except 300nv2. nothing works with that to to the proprietary drivers used.
before complaining that this is a 15 year old adapter and is hard to find. you may find one on ebay.
and thank you for your contribution. I myself could not eloquently describe or went as deep as you did.