I find speaking/writing in E-Prime challenging. Doubly so when I endeavor to remove all forms of words expressing "possession" or "property". I also find these things fun and valuable, at least as exercises.

finds this bit rather silly: Bourland sees specifically the "identity" and "predication" functions as pernicious, but advocates eliminating all forms for the sake of simplicity.

Clearly, it doesn't lead to simplicity.

About the "class inclusion" function, it would be challenging to build ontologies without the concept "A is a B".

I'm not just criticizing. I'm increasingly wary of statements of "essence", preferring instead statements of "function/action", particularly where people are involved.

So I understand at least some of the motivation for E-Prime, but I think it's misguided.

That's fair. For me, in part it's (<- "to be" in "it is") just a way of raising awareness about things I normally/previously don't/didn't pay any attention to... and that do have impacts.