I think the cost of the complexity is too high. I much prefer simple code that provides 90% functionality to 10x more complicated code that provides 98%.
Generally I think OS-bundled tools that may be used for stream processing of large amounts of data (like grep) should skew further towards performance, because there are a non-trivial number of people passing gigabytes of data through grep every day and a 10-20% performance improvement there is a significant boon to global productivity.
Tools that solve a very specific problem and do it with a strong expectation of correctness and performance are what makes *nix environments so powerful - not only can you throw together a nifty bash script that duplicates the functionality of a massive cluster operation, the script may actually outperform the cluster because of how performance-focused those tools are!
I see this issue as being a bit similar to high- vs. low-level programming languages. Could we write absolutely everything in JavaScript and probably have a lot of the code be more readable than it'd be in C or Rust? Absolutely. But that doesn't mean it's not worth using C in some cases to make the program perform well on hardware that doesn't have enough firepower to just ignore the overhead, and it doesn't mean it's not worth using Rust in cases where stability is absolutely required.
I literally can make no sense of that. Why do you think widely used pieces of software should not be well made.
The core is about 70 lines. As for over-optimising it, I think chesterton's fence needs mentioning https://fs.blog/2020/03/chestertons-fence/
I don't think this is a useful avenue of debate for me.
As a user of the software, which would you rather have, 90% or 98% functionality? Also the number of users outnumber the number of coders by orders of magnitudes.
I for one am well chuffed that the emacs team are so hardcore about bugs.