It's functional - yes, intuitive - maybe, but optimized is highly debatable.
The answer to maintaining a highly functional and stable OS is piles and piles of backwards compatibility misery on the devs.
You want Windows 9? Sorry, some code checks the string for Windows 9 to determine if the OS is Windows 95 or 98.
He was talking about user interface not app compatibility
Millions of total computer noobs hit the ground running with Windows 95. It was a great achievement in software design.