

Biphasic/Polyphasic sleep by itself isn’t anything bad, and it is a technique some use for getting the same amount in less total time. Humans didn’t really start consistently sleeping 8 solid hours in one go until the industrial revolution or so.
For me personally, while normally I’ll do 8-10 hours, if I’m extremely tired from like an all-nighter or something, I will get exactly 4½ hours of sleep at first, always, without a doubt. I’ll then wake up unable to sleep until after roughly 6-8 hours of being awake at which point I’ll crash and have to go back to sleep.

Not just the second sleep theory, though I’d argue it isn’t exactly just a “few peoples accounts”, but stuff like siesta and naps in general.
The point isn’t to say everyone slept the exact same biphasic sleep before but that after the industrial revolution the shift has been for everyone to transition to the “8-hours at night in one go at exactly the same time” method, which doesn’t suit everyone and isn’t exactly natural. Before artificial lights and clocks people slept with way more irregularity as there wasn’t any strict time schedule to follow, and people waking up during the night or not getting enough sleep at one go wasn’t really such an issue.
Not to mention that your sleep would have to follow the seasons and the sun way more.