First off when I hear a report of severe or extreme turbulence along my route of flight I will do everything possible from flying through that area. I see no need to question the report. I realize that nearly all pilots have a huge ego and to be honest I'm no exception, it comes with the territory. However, when a pilot chooses to ignore or disbelieve a report of severe turbulence because of the type of aircraft or type of operation the reporting source is to me the height of 'Big Aircraft' arrogance.
"Oh that was just a biz-jet, with a couple of inexperienced pilots, they wouldn't know severe turbulence if it hit them in the face." Chuckle, chuckle, nudge, nudge, wink, wink.
I have encountered severe turbulence, or extreme turbulence three times in my 40 years and 21,000 hours of flying. In all three encounters it was CAT, twice I was flying a 727 and the other occasion a Sabre 65. In all three cases the autopilot kicked off, the instruments were for all practical purposes unreadable and the aircraft was nearly completely out of control. On the two cases in the 727 we did have members of the cabin crew injured, one was hurt when the life raft stored in the overhead fell out and broke the collar bone of one person and on the other occasion a person broke his ankle when he was thrown up against the overhead and landed on his foot the wrong way.
By the way, on all three encounters there was no reports of turbulence other than occasional light to mild.
Severe turbulence is out there and ignore the reports at your own peril.