More to it than that

Robinson fired Fritz Shurmur after the 1990 season. He hired Fisher, specifically to bring on a 4-3 defense that featured the 46 defensive scheme. Then Rams didn't bring in many good players that fit the scheme. Greene was a square peg in round hole.

While the Shurmur Eagle defense was identical to the 46, who played where was an issue. On 3rd downs Greene rushed the passer like he always did, but he played running downs in the Richard Dent position, on the right side, sometimes in the 46 other times in the 4-3. So it was not a good fit.

When Knox was hired he had Dyer run a basic 4-3 with Kevin at LLBer in base and a DE in nickel, but usually Kevin played it from a 2-point stance.

Kevin's true calling was as a 3-4 OLber. With Shurmur he was that, but in the Eagle (46) he was even wider and didn't have to do any coverage

Also, in 1991, under Fisher, there were lots of injuries on Dline and Greene had to move back the 4-3 LBer on run downs, etc

Like Kevin a lot, but to say Fish changed schemes when it was Robinson who canned Shurmur and wanted Buddy Ryan's defense is an error