I have no idea about Diablo, but honestly now…
All things being equal: Tokens for the armor type you’re playing have 1/4 chance of dropping. Tokens for “everything but” have a 3/4 chance of dropping. They’d have to actively increase the droprate of the type your character can use for the game not to drop them at a lower rate. No nefarious conspiracies required.
My druid’s bank is literally full of BoA tokens. Of all types. I’ve fully outfitted a warlock, paladin, evoker, and druid, and fully done a hunter just to unlock the mog. And it’s STILL full. Like, full full. As in, the main bank and all of her bags in the bank are full.
So. Many. Tokens. Drop.
I do wish there was a vendor though. I get like no cloak tokens, it’s annoying cause they bait you with a cloak token to not do the skip, but I want to do the skip. 
Cloak, Trinket, and Weapons don’t really drop for me.
Why can we not just buy them from a vendor for Elemental Overflow? I have literally nothing to buy for Overflow anymore. Can we please get a vendor that lets us buy them for like 2000-5000 overflow each? X_X
Also, the Upgrade Books need to be made BoA.