It has been a poor season, no doubt but using the term embarrassing to describe the players numbers other than Cox and Amir is a massive exaggeration. Adam Rossington has been able to play T20 around the world with a career average of 20.79, SR 144. Scores are a bit higher now but Pettini averaged 27, Ryder 24, Bopara 29, Foster 21 and Wheater 19 over their T20 careers at Essex.
I understand that batting averages in this format cannot be compared with red-ball, and that anything over 30 is decent. I can't take that Rossington stat very seriously I'm afraid - doesn't it show that you can burgle a good living in this format rather than say anything about where we should set the bar. Of the other players you mention, Bopara's 29 is probably a bit below par for a player of his ability. I am surprised that Pettini averaged 27, fair play to him. Ryder's 24 should have been higher, but his compulsion to hit in the air limited his effectiveness.
Looking at current top order players this season we have Pepper averaging 28, Cox 38, Walter 23, Elgar 26, Benkenstein 19, Allison 15, Critchley 13. Maybe 'embarrassing' is a bit strong in some cases (though not in others) but I would maintain that Cox is the only one who really performed. Pepper averaged 45 in this tournament last year, so while 28 may be OK-ish it still represents a major falling off. Benkenstein's numbers are OK for where he bats, but I found him very frustrating to watch, felt he was often trying to be too clever with ramps, reverses and the like, usually missing the shot. He has time though.
Plus of course all this talk of averages misses the context e.g. Harmer averaged 17 this year, which is probably quite good for someone batting in the lower middle order, but that was largely thanks to his quickfire 50 in a game that was already over.
