X220/X230 still has 2/4T cores, up to 16GB of RAM, and both mSATA and SATA ports for SSD upgrades. They also have IPS displays.
It was only five years ago that Intel moved their i5 and i7's from dual cores. Some lower end machines still have these core counts. These are still viable machines.
I think this is as far back as most people would be comfortable with on a daily basis. One could still run modern desktop environments (KDE/Gnome) on these systems and browse the modern web without any tricks (adblock, disabling javascript).
That modern smartphones are more powerful only shows how overkill modern smartphones are, where the profit margins are, and how bloated our mobile operating systems have become. Why do I need more processing power to have less ability to do things on a smartphone?
Regarding the author's (now 18 year old) machine, the author explains their workflow and how using a minimalist distribution for older machines works for them. I wouldn't recommend this to any casual user however, but it also shows how one can make the most of what they already own.