I don't think he's criticizing the lack of longer bios but rather how the bulk of our understanding of champs are explicitly TOLD to us through AMAs.
For example, the Shyvana Creative Design AMA:
http://forums.na.leagueoflegends.com/board/showthread.php?t=2424681&page=6#post27710253
Granted, it's an AMA specifically for creative design by look at the GOLD MINE of information on Shyvana we have here.
She respects all of them, but they may not be entirely friendly. Garen, for example, finds Shyvana to lack the principles that truly make a Demacian warrior. He values discipline and self-control, and in his mind, Shyvana exemplifies none of this. He'll fight beside her, but he may disapprove of her methods.
Shyvana probably finds Lux youthful and distant--Lux hasn't yet become a true warrior. Of the three of them, she probably gets along with Xin Zhao the best (second to Jarvan, of course).
There's a flaw to Shyvana in that she doesn't quite actively seek out people who might accept her--she tends to assume the worst of everyone she encounters. She always has her guard up.
This is all neat stuff.
There's just one problem:
**It's TOLD to us. **
We, the audience, aren't given a chance to interact with the lore at all here. All of Shyvana's supplementary materials doesn't indicate any of these - the contrast with Garen on warrior philosophies, Shyvana's relationship with Lux or how Shyvana doesn't approach people... none of that is ever indicated in the written materials.
We aren't given short stories or anedoctes where we try to extrapolate information... we aren't given details or context clues... we aren't allowed to even try to think.
It's flat-out TOLD to us.
That's horrendous design for a NARRATIVE department.
Please note this is from 2012 - they've had plenty of time to release additional supplementary material for Shyvana if they so wished that actually included these facets of her character -which have not materialized.
And you see this is a recurring trend. A lot of the information we know about champs has been straight up spoon-fed to us. Tham Kench is a demon - or something - okay, we could have figured that. Wait, he's friends with Aatrox...? Um... is he a Darkin? Nope - more vagueness from red posts.
When the bulk of what we know about champs require essentially author's notes clarification because the original author didn't think too hard on what information s/he wanted to give the audience in the original bio or lore pieces then that's a problem.