I've been farming FGs with Instosis, and I have been getting at least 5 cards per hour and once even 4 cards in 10 minutes!
(Yes, this was only a few days back)
However, I did get a little frustrated, and sometimes had no-card streaks.
Even so, I doubt that card rates has gone down since the arena update.
Oddities of Elements the game. Did you ever win 3 cards in one spin?
I'm guessing you mean one 'win' instead of one 'spin.
I've gotten 2 cards plenty of times, but never 3.