That's a very common pattern. Special characters are usually allowed only from a predefined list. I don't see how this is specifically bad or deserves a blog post.
Why limit it in such a way? if the backend is so fragile it can't handle a + sign then it is bad
As for the blog post it was just a way for me to get some frustration off my chest. It's also posted in the "Scraps" section of my site, which I just use for short one-off things like this. If I then decide to write an article about it later (like a longer thing about password managers and dealing with passwords online) then I could link to these scraps.
And let me tell you about the 'super strong password' your generators create: they suck
They suck if you have to deal with any kind of escaping (like in a shell script, for example)
They suck if you're unsure of the current keyboard layout you're currently using
Easier to take out some character classes instead of having to solve support tickets