.... I got rather fed up a while ago when so many other photographers were telling me that "all 2x TCs" are slightly soft. Until, I saw the results a friend was getting on his Canon EF 500mm F/4L II with a Canon 2x III (version II Extenders are not so well matched). So I took the plunge and bought one and have kept more shots with the 2x mounted than either without or with the 1.4x. So, I'm sorry but I'm not going to take your word for it. Olympus have developed both MC-14 and MC-20 very specifically for their 2 PRO lenses (and also the MC-20 for their forthcoming super telephoto zoom).
For what it's worth, a very successful professional wildlife and landscape photographer friend after many years with Canon bought Nikon and was so disappointed with Nikon's TCs that he returned all the Nikon gear and is still with Canon. I hasten to add that it was only the TCs from Nikon that he was dissatisfied with. Btw, he's not inclined to go mirrorless... yet!
I don't know how distant your "distance subject" is and your term unless "relatively close" adds to a suggestion of significant limitations. But I think it is only at the more extreme long distances that a good TC loses any image quality. Atmospheric conditions also play a part, plus the extent of enlargement a photographer applies to their original image.
I have a MC-20 on order and will certainly report and display my images for people to judge for themselves. I will be returning it if in the unlikely event I am not satisfied, but then again I might be more easily satisfied than some (aka pixel-peepers)
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Shot on Canon D-SLR and also EOS mirrorless, here is an album of my best efforts with a 2x :
https://www.flickr.com/photos/114775606@N07/albums/72157685377629534
Olympus are openly really taking on Canon, Nikon, and Sony with their M1X system and simply cannot afford to get their MC-20 TC wrong - TCs are an essential component in a wildlife photographer's kit.
I think it is up to the individual photographer to realise that there is no such thing as a perfect camera or lens and to limit their demands on their gear accordingly. From experiencing that m4/3 does not yield good results as easily as full-frame in poor light, I simply accept it and take less photos - Go for quality rather than quantity.