Thatās a very valid point. It needs a bit of effort to not letting the machines become obsolete because of the software side of things. Itās doable, but you need to be very deliberate about it.
Iām still running most of my graphic design business on a mid 2010 Mac Pro, with the lousy AMD 4870 GPU and only 12Gb of RAM. Of course I donāt do 4K Video editing, and my use of Blender is very limited. Most of the Adobe CC applications which I heavily rely on, run just fine and I can keep Photoshop, Illustrator and other stuff open at the same time. I usually refuse to update if I donāt have to. Last year I updated to Sierra because some software would not run anymore.
I could probably keep using this for a bunch more years, except I need to update to Mojave for a project now, but Apple wonāt let me, because of Metal.
So Iām getting a Mac Mini and will perhaps expand it over the years with some more RAM and an eGPU (though I need to figure out if the latter will be worth it).
I have the feeling that itās getting harder to keep these machines from falling into obsolescence, right now itās probably still doable if you restrain yourself a bit, but who knows what the future will bring. What will the computing landscape look like in 5 years? And in 10? Hard to say.
Itās been often said that the Mac Mini is the Mac Pro for the rest of us. Itās relatively upgrade-able and has a good value for the money. I hope I can make it last at least 6-7 years.