The 8088/8086 did not have an MMU.
It did not provide memory protection.
The PDP-11 MMU provided memory protection so that process isolation was possible, but its main function was also addressing space extension, from 16-bit to 18-bit in the first version and from 16-bit to 22-bit in the later version, but that function was much less convenient to use than in 8088/8086.
The 80286 is generally considered to be when an MMU was added to the x86 line.
Adding flags for additional features piggy-backed over the address translation, e.g. memory protection, is the easy part of a MMU.
80286 added memory protection, which is essential for a multi-user operating system, like UNIX. That is why it was the first Intel CPU to which UNIX was ported, but any computer with address space extension must have a MMU.
8088/8086 was indeed unusual in having a MMU without memory protection, because it was intended only for personal computers, while the previous computers expensive enough to need address space extension were all intended for multi-user applications, so all included memory protection in the MMUs.
So, no. That's not what any of the rest of us mean by "MMU".
You can run the system in your browser using the pcjs emulator: https://www.pcjs.org/software/pcx86/sys/unix/sco/xenix/086/2...
In hardware this is literally an add. Calling a single add (with aliasing) an MMU is quite a reach. The 80286 is not merely an extension on this as the segment registers actually do indirection. Also in terms of silicon real-estate I think you greatly underestimate the complexity of what you call the “easy” part - anything that can fault is no longer trivial for one - the 8088 cannot do this.