Feels like we remember MS-DOS as simple because it fit the time. One user, limited hardware, not much going on in the background. As soon as you try to add multitasking, networking, or even basic isolation, that simplicity doesn’t really hold up.
Then you read some "under the hood" book or source code and start stumbling upon decade of hacks upon hacks to keep this cart rolling while computer revolution was happening in the background.
One example: IBM in its infinite wisdom didnt expect to support more than one type of floppy in 5150 BIOS. IVT (Interrupt Vector Tble) has allocated space for only one DPT entry (Diskette Parameters Table), same goes for DBA (Bios Data Area). Few years later 1.2MB 5.25 drives showed up, year later 720KB 3.5 ones and so one. As a result BIOS was forced to play musical chairs under the hood constantly shuffling contents of that _one DPT entry_ replacing it on the fly while trying to keep track of whats going on. Of course DOS needs to run on older PCs without multi floppy format aware BIOS thus 1986 MS-DOS 3.2 introduced DRIVPARM doing exactly the same shuffling one layer above https://jeffpar.github.io/kbarchive/kb/060/Q60091/
DOS was build one small hack at a time. High Memory, Upper Memory, Expanded memory, Extended memory, A20, exit from Protected mode, more than one kind of floppy, hard drive, more than two hard drives, the list of kludges just keeps going.
Or even "little multitasking" because while Windows had multitasking, we didn't have the HW to do too many things at the same time.
Right now we're on the crazy end of that spectrum. Every tab on your browser is potentially an application, and we multitask like crazy on it.
Do I want to go back to "No multitasking?" Not really. Or at least not all the time. But I definitely want to put barriers. Such as taking a minute to switch windows/applications.
Also the days when you turned on a computer it was ready to rock within two seconds. A few friends were discussing video game load times throughout the years. Overall the elapsed times haven't changed much at all.
GEOS was pretty cool too - amazing what you can fit in 64K if use a big enough hammer :-D