Which would be fine if the device still did what you want it to do. But in fact connected electronic devices do go obsolete as soon as vendors stop providing security updates.

No, they aren't. That hasn't been even close to true for many years.

For example, I work with some very high-end PC workstations (think multimedia, 3D modelling, that kind of thing). Sure, the new spec ones are a bit faster, but if you look back those 4 years you mentioned, there really isn't that much difference.

The price/performance sweet spot back then was probably an i7 2600K. Are modern CPUs faster? Sure. Are they an order of magnitude faster? Not even close. The main emphasis in recent years has been on lower power/heat and to some extent on increasing core count particularly at the high end. Actual per-core speeds or instruction processing has improved only modestly. And in most applications, they were already so powerful that you wouldn't even notice the difference.

Graphics cards are a similar story. Of course modern cards are somewhat faster than their counterparts from a generation ago, but unless you use the most demanding software, the card in that i7 2600K machine probably still works just fine with today's applications. Again, most people wouldn't even notice the difference, because the baseline level was already high enough.

The amount of RAM typically supplied in modern PCs hasn't much changed, so no huge jumps in capability there either. In fact, I'd say storage and networking are probably the only major areas where speeds are dramatically better today than they were four years ago in most western economies. This is largely because it has become cost-effective at mainstream levels to use things like SSDs, fibre broadband and 4G mobile networks where the previous generation of devices at a similar price point would have used spinning platters, old phone lines and 3G. These changes really do render the previous generation of devices obsolete at a similar price point and really do make a substantial difference to what an average user can do with the new equipment.

The only other area where there have been dramatic improvements, not in performance but in capability, are displays. The 200+ ppi devices previously reserved for high-end and physically small mobile devices are now widely available in laptops. Your new 48" TV might show 4K material natively. But again, this only helps if you have content to look at that can take advantage of the finer details, which a lot of people won't, so I'd hardly say it makes a good display from the previous generation obsolete.

The 4S is another example of an older device that competes really well with modern hardware.