Porsche owners have a lot of mental baggage. Changing from a flat 6 to a flat 4 hit a nerve in many older fans.
Ostensibly they complained about the sound "not sounding like a Porsche". Yes it was an incredible an mount of whining. I stopped reading competing forums for a long time because I was so tired of the shrieking...yes..this horse is dead and decomposed at this point.
There were also a number of other complaints about the new 718. Porsche owners are notable for their need to complain about every change Porsche makes, no matter how insignificant or immaterial. There were those who complained about the new interior looked cheaper, the car weighed more than the predecessor, the rear spoiler didn't look right, the front spoiler was ugly....I could go on for an hour about all the trivial complaints I have read about the new 718. None of which I think is anything other than whining from a butthurt audience who have too much free time on their hands and aren't really what I would call "enthusiast" but rather "self absorbed".
To me, the worst part of owning a Porsche is the is the reputation Porsche owners have. I've never had anybody say anything insulting or offensive to my face but I have read so many stupid comments by owners that I feel it cheapens the Porsche experience. I suppose it is funny ( but really not) that a few weeks ago I went to Porsche dealer to look at a car. The manager came out after hearing that I own three Porsches and said " I hear you are a Porsche guy" I actually almost told him to go F*&^ himself, I thought he was insulting me....LOL.. Good thing I caught myself before I did. He was just making small talk but I really didn't like being associated with the brand, even though I enjoy the cars and my dealer, PCA, PCNA, Euro delivery, track school, and PEC have always treated me splendidly.
Ok, back to the issues with the flat 4...
I think a main reason for the complaints are beyond the sound. I think it is undeniable that many people buy a 718/Boxster/Cayman because they cannot afford a 911. Sure some people love the mid engine platform but to many it is an affordable substitute for the 911 of their childhood dreams. The further the 718 gets from the 911, they more people complain about it. The early models 986/987 where pretty much built from leftover parts of the 911. The 981 and subsequently the 718 the car started to become a separate entity from the 911. The less the car is a "poor man's 911" the less it has that 911 mystique. For me, I like it because of what it is, for many Porsche owners they disparage it for what it isn't.
I am 99% confident Porsche will not switch back to a NA flat 6 in the 718 ( although I would like a Turbo F6). There has been speculation about that for years. I would love for them to switch back, it would make my torquey little monster that much rarer and I think they would become a cult classic. IMO, it would be a major mistake for Porsche to accept lower performance to satisfy the complaints about the sound. No doubt a new flat 6 would weigh more and there would still be forum dwellers would find a number of other things to complain about the new car.
Finally there is the "resale" issue with the 718. I don't know if this is a real issue. Many think the 981 has kept value at the expense of the 718, I don't see it in my experience. I, personally, plan to own my cars for too long to worry about resale.