Ashkan, I've been following your post for a while, because you seem to have been "cycling" finasteride for a long time. I saw people discussing this long ago but you're the only one actually doing it with success.
As you mentioned, as time goes, finasteride loses its effect and the sides build up, usually at the two year mark you have to drop it and reboot it several months or a year later. In the meantime, whenever you go back on finasteride, you were able to regain what you lost during the off period.
I've been pondering this topic for long. finasteride losing effect seems common. For most people it happens at around the five year mark. I experienced the same. For some people the sides don't build up, for some they do, and when they do, it's usually mental related.
I believe androgen receptor upregulation plays a big role in it. There has been speculations on this for years.
AR regulation not only explains why finasteride loses its effect, but also gives a possible explanation to the myth of post finasteride syndrome (well considering the solid evidence of PFS it might be unfair to call it a myth). When you're on finasteride your body upregulates ARs to regain its homeostasis. After you quit, your body has 300% DHT which is overwhelmingly high and causes a intense down regulation of ARs, which goes to different extent in different tissues. For some reason the ARs in specific parts of the body never bounce back to normal even when the general androgen signalling returns, thus PFS.(Summarized from a solvePFS thread discussing restoration of androgen sensitivity)
I think finasteride does give you tolerance. There's no way a potent 5AR used long term won't do that. Actually if we consider the steroid cycling approach of body builders, it makes much sense to go off finasteride every once in a while to maximize its effect and minimize sides, especially when you notice side effects creeping up, which indicates you're body has been deprived of androgen signalling substantially.
The problem is we don't know the exact safe approach to do this (unlike steroid users who have more or less empirically agreed cycling plans). We don't dare risking losing hair on that off cycle either. You mentioned you were losing hair in a diffuse pattern, which can be more easily regrown. However for those losing their hairline in a intense way this may not work out...
finasteride is the devil's potion!...
(BTW as I remember you were looking into seti too. Are you on it now?)