80186 introduced some instructions for HLL features. 80286 introduced some instructions for protected mode, and provided some multitasking ability with external MMU which was never intended for PCs but servers/workstations, but the protection mode and addressing line was implemented in a rather different way from the 80386 family. So what has really been inherited from 80286? Shouldn't we regard 80386 as the direct descend of 8086/80186, rather than 80286?
You are getting everything wrong.
The 286 has integrated segmentation unit and protected modes to allow multitasking OSes and more memory (up to 16MB). It was actually used for that purpose in early versions of OS/2 and Windows.
The definition of "workstation" is arbitrary. 640kB DOS was becoming cramped, and the 286 allowed to use more memory.
The 386 had two important enhancements : 32bits registers and a pagination unit. The pagination unit allows virtual memory and is more suitable for common UNIX-like OSes which aren't well adapted to x86 segmentation. i386 paged MMU is architected between the segmentation unit addresses and physical memory.
The 386 supports all of 286 protected modes, they can be used in 16bits environments (and many, many 386 ran for years in popular 16bits OSes such as Windows 3.1), and in new 32bits protected modes (such as the WIN32 extension for Windows 3.1).
Since the introduction of AMD 64bits mode, and a bit before, segmentation concepts (with complex stuff like call gates, segment limits...) were a bit obsoleted as pagination is good enough for multitasking OSes, and more compatible with RISC CPUs which have no concept of segments. (rough simplification)