Something you have to keep in mind is, Demand growth is not linear. The experience we enjoy today, similar experience 3 years down the line, I doubt A12 will hold just as well as it is today. Website loads more stuff to support whatever. Video streaming uses different codecs that benefit newer devices more. Even for your so-called "basic" tasks, older electronics may not be able to comfortably handle it. Yes, YMMV, but past 3 years is not the same as next 3 years, and I tend to be conservative on this one.
Also, calling "OP has at least 3 years of comfortable use out of the device" as "truth" in and out of itself is already a stretch. I'd call them "educated predictions" or simply "opinion", cause we have no idea what will happen exactly in the next 3 years. Your overall demand may remain relatively stable, but that's not what the tech world goes.