Uhm, I doubt you can say its easy to shuffle. Heck, I bet most of you here separate your decks in two and shuffle them like that.
Thats a problem, don't deny its there.
Nope, I don't cut it in half. I single sleeve and have large hands, so it's not an issue for me. Even if it was, you could always table shuffle.
You want a deck too big to shuffle? Years ago, I had a friend with a 300 card Prismatic deck that he would play against 60 card decks. He bought one of the white cardboard boxes and had to mash shuffle cards into the box because the deck was simply too big to handle (don't worry, the sleeves protected them). And he did it by choice, no complaints.
So, yeah, I do deny that 100 is a problem that could be solved by dropping to 85.
Brands would still sell packs of 100 sleeves (they did WAY before Commander was this popular).
Did they? Aside from penny sleeves (which I doubt a person who double-sleeves would ever consider), I'm fairly certain they only sold packs of 80 or 60 before EDH/Commander became popular. I recall quite clearly people being frustrated that you couldn't sleeve a Commander deck without buying too many or too few.