Hair grows in cycles. One individual follicle starts pumping out a new hair, and at this beginning phase the hair shaft is at its most thin. The hair continues this growth phase for several months, and as it does so the hairshaft gets increasingly thick. When the hair growth cycle has ended, the hair remains in the follicle, but is no longer growing. This lasts a few more months. Then, the follicle releases the old hair, and at the very end of that old hair is a bulb. That bulb end of the hair marks the very thickest that that particular hair will grow. If the follicle is sensitive to DHT, then as the next hair grows it will come in ever so thinner, and when it spits out the bulb the bulb of hair two will be markedly thinner than that from the first bulb.
Thus, I would say that when examining hair quality over time, the only real accurate way to determine trends is to ONLY look at the hair with bulbs on them. If your shed hair bulbs are getting smaller, then your scalp is going to hell
If you are shedding hair without bulbs, then it indicates to me a different issue. Either your hair has just gotten too brittle or breaks easily. BUT, you can't judge too much from a bulbless hair. It might have broken off from a hair early in its growth stage, which would be completely normal as young hairs are naturally at their thinnest. Or, it could have broken off of a hair that is fairly close to coming to rest, which is when that hair is supposed to be at its thickest.
Unless you know exactly where in the growth stage that particular hairshaft was in, you cannot judge too much from it, in isolation.