Pilot flying into OSH reported an NMAC during approach resulting in a go-around. Reporter stated ATC controllers need better knowledge on performance limitations of certain aircraft.

Narrative

Arrival to OSH. Flight of X number of aircraft following high speed approach 135 kts. 2300 ft. AGL Runway 27. I was flying #2 position echelon right. Approaching the downwind leg the flight was told to slow for traffic ahead. Controller continued to ask for slowing. Lead aircraft of flight slowed flight to about 100 kts. Lead aircraft fell out of flight in descending right hand turn. I called out to controller 'Unable speed' and controller continued a dissertation on how 'everything works better if we could learn to slow down'. Controller was obviously not familiar with 'Unable Speed' terminology. I assumed lead aircraft of flight and picked best angle to another aircraft ahead to provide spacing from the flight. I turned base leg to final with what looked like perfect spacing from the aircraft ahead and IFR traffic was then cleared to land 27 after the aircraft ahead. Aircraft Y passed off my left wing less than 100 ft. horizontal spacing 0' vertical. I executed a go around and controller asked 'where did you come from'? Somehow the controller lost track of our aircraft. I entered the downwind leg again and I was cleared to land as well as other aircraft in trail. The aircraft that was originally the lead reentered the pattern behind us and was cleared to land. The controller yelled at our original aircraft lead to turn off into grass ASAP more than once. The pilot finally responded on the radio 'Unable' he must exit on hard pavement. The quality and experience of ATC has declined to a frightening and nearly catastrophic level. ATC inability to identify aircraft and their limitations or understand 'Unable' is inexcusable. They have a low speed approach and a high speed approach for a reason. My speed on final is 100 kts. and touch down is 80 kts. I cannot follow slow aircraft and neither could our flight. This needs to be addressed and fixed before it kills pilots and passengers.