Cheese is a definition that depends on gaming social contract and the environment in which the game is played, so it is a hard question to answer. That always has to frame the answer. In my opinion, in a tournament like environment it is no different than Tau focusing on shooting, grey knights focusing on psykers, etc., with a possible exception that to do it optimally, freakshow generally can/will pull from so many different sources to pull it off, and more sources adds to the cheese stigma.
If it were DE alone, it would be interpreted like our poison weapons.
FWIW my own personal misgiving with it is that I'm concerned that Eldar+Harlequins generally "do it [freakshow] better" than pure DE or DE + harlequins alone would (essentially adding insult to injury with the other things they do quite well). It miffs me that DE are essentially a glorified WWP + LD aura caddy. Given how available telepathy is to Eldar, did they really need the ATSKNF exception on soulfright? Really?