I recently dug out a 2013 MacBook and I’m surprised at how slow it feels. “Unusably” is of course a subjective measure but I think if I was using this day to day I’d get annoyed.
Source: I just did this with a 2011 MacBook Pro
Thr issue that mine has - aside from a broken hinge over time - is that one of the thermal sensors is fucked, so the machine puts the fans on full and heavily throttles the CPU. Before that happened (last year) it was a solid machine.
Consider that the utility of old hardware depends on what you want to do with it, as well.
I have Debian on both but recently I was testing old SSDs and one had windows 10 and even that was perfectly usable.
My main daily driver is a MacBook Pro 64GB M2 Max, so it's not like I live in a world of ancient tech and don't understand the difference.