Earlier quoted context omitted.
I find it bizarre that most people don't realize writing 'correctly' is just intelligence signaling too. There's no reason for it most of the time. If I can type something faster but still just as clear by typing it less-formally, I will often do so.
"but still just as clear" is a critical qualifier in your sentence. With that stipulated, I agree. When that is absent is when there's an issue. This is a not a matter of "Never end a sentence on a preposition." "This is the type of errant pedantry up with which I will not put."
However, I've seen people us abbreviations that are incredibly difficult to parse, even for people with English as a first language. I can't imagine how difficult some of those emails can be for people that didn't grow up with the language.