I indeed make this very error, but I prefer to rely on tools such as Grammarly to help me improve my abilities, than to other people to start accepting my mistakes as basically the natural mutation of the language.

Yes, a language mutates, and a simple language may be more welcome, but we don't need to force it. Let it happen naturally.

It is, in fact, perfectly understandable to say “less errors” rather than “fewer errors”, except insofar as doing so marks one as “uneducated” and déclassé compared to someone who uses the “correct” usage. Of course, this particular class marker is less meaningful now that it’s too widely known—it’s more likely a marker of someone being a member of an anxious and pretentious tier of the middle class by now.

The pointless difficulty is, in fact, the point. For similar reasons, the word “ain’t” and the double negative are perfectly well-attested usages; they just exist primarily within specific dialects that are not socially prestigious. (Of course, blatant and well-known markers of class status are seen as stuffy and pretentious, which is why politicians tend to code-switch into more “folksy” dialects.

As for competing with Mandarin, I’m sure the Chinese upper classes are just as capable of telling each other apart from the rabble.

What makes English actually difficult to learn is its broad vocabulary of idioms. One needs to develop a sense for 'natural expressions' because often there are dozens of grammatical expressions, only one of which feels natural. This is something difficult to understand for a native speaker so let me give you an example. Which if any of these expressions are a natural way to get a teacher's attention? 'Can I have a question,' 'may I have a question,' 'can I ask a question,' 'can I ask you a question,' 'may I ask you a question,' or 'I have a question.' This is by far more difficult to learn than any rule of grammar.