For microneedling on the scalp to work, the wounds need to go deep enough to sufficiently damage the collagen(fibrosis), so that the body can replace it with healthier tissue. The scalp is a lot thicker than the facial skin, and even with Dermatology, to resurface facial scars with microneedling, you need to go DEEP. With the scalp, you need to go even deeper. Frankly speaking I genuinely don't believe many people who needle their scalps go deep enough. It sounds like you do, but I've seen people try to get away with 0.75mm dermarollers, over top of hair, and it's mind boggling to me how they think that will be effective. I'm sure shallower wounds can also stimulate growth via bloodflow, but I don't think the "true healing" occurs unless the wounds are deep enough to break up that fibrotic (excessive collagen) tissue.
It is understood how balding happens. Balding areas of the scalp have up to 4x as many collagen fibers (fibrosis), and the effect of this is the restriction of bloodflow, likewise DHT also acts as a vasoconstrictor (anti inflammatory action?) and likely causes the collagen to build up. When bloodflow becomes restricted so much, the hair follicles essentially shut down. When balding people stop using minoxidil, they really only lose their hairs they grew with it (in the regions of their scalp with lots of fibrosis), as well as the areas which would have build up fibrosis during that time period. They don't tend to lose the hair in other regions where they weren't aggressively balding.
Minoxidil doesn't stop the build up of fibrosis, but DHT-blockers do. There are a number of people on reddit /r/tressless who reported stopping Minoxidil while on finasteride, and they stated they lost all their minoxidil hair, but they kept their finasteride hair. This indicates that the hair simply falls out in the regions the scalp cannot support it.
That beard thread you're talking about, the one that was 500-700 pages or so, I had spend close to 2 weeks reading through the entire thing, prior to doing it myself. Looking at the results of literally hundreds of people. Pretty much every single complaint of beard growth loss was from people who didn't continue use for long enough, and people on the thread pointed this out. There are warnings repeatedly about this, that if people do not keep up use long enough for the hairs to reach terminal maturity, they WILL lose their gains. This is the general consensus of Minoxidils actions on the beard - it stimulates vellus/dormant hairs for long enough until they reach terminal maturity - if minoxidil is ceased prior to that, you will lose those hairs upon stopping.
It is typically recommended people go for at least 9-12 months or more, to ensure their hairs are able to reach full maturity, though some people get away with less time. As far as I remember, the one thing people who complained of losses had in common was that they'd often quit after 3-4 months or so after they see growth they are happy with, which is not generally enough time to keep gains for most people, especially in virgin beard areas (missing connector regions usually, etc)
However this whole vellus ->terminal hair thing isn't that relavant to scalp theory, because our main issue here is Fibrosis/DHT.
I understand your concerns. I'd like to clarify that most of what I was talking about was using Minoxidil (low %) to rapidly mature your blonde vellus hairs that you have grown through needling. It looks like your progress is coming along quickly anyhow, so if you're okay with the rate you're going at, then just keep that up. I was just saying if I was in your shoes, I'd personally opt to throw in Minoxidil just for the sake of speeding up growth, while keeping up my needling/finasteride efforts.
