Disclaimer: This is a broad generalization when referring to specific episodes but I am making an overall point so don’t dick me over some late night show which you term a classic.
Each decade of television (and radio) has had an element of the radical that has changed the landscape and influenced the following generation from the Goon Show (1950’s), Tony Hancock (1960’s), Monty Python/ Q (1970’s), Blackadder/ The Young Ones/ Only Fools and Horses/ Spitting Image (1980’s), The Day Today, Big Train (1990’s), The Office, Nighty Night and Nathan Barley in the noughties.
Obviously there was a load of crap that fell by the wayside (Fresh Fields/ Curry and Chips/ Mind your Language) but the last one on my list is the point I am making albeit a broad one.
For me the last great comedy series was Nathan Barley and due to it’s reception was considered an artistic failure, which seemed to be a Chris Morris backlash. Since then there has been nothing challenging which is curious because comedy is about as fashionable as Anna Wintour these days.