@OP, I do not think the forum community has the data to fully answer that question, considering devs also play alt accounts. But I'll throw a guess and say 3. Exactly 3.
But, putting your question into a rhetorical context, I feel it's irrelevent because being an artist or game programmer doesn't automatically make one an expert gamer. Writing your own game won't make you the best at it. For example when World of Warcraft gamers had already completed the first raid dungeon when the game released, the developers who wrote the mechanics of the dungeon hadn't even downed all the bosses yet and were utterly amazed at the skill level of their player base. Programmers write code, artists draw, gamers play games.
They're looking at the rewards from a cost perspective. How many rewards can they afford to give away without diminishing the value of the items too badly? Throw the players a bone and give them a chance to win something nice, but don't just give it away. They just finished giving away hero mechs in the form of L variants.
I dunno, I think a TBR champ is one of the best free prizes that a no-cash player can hope to win so I would hope the scoring requirements reflect that.
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Edit - Just saw they lowered the requirement from 250 to 150. I take back the comment about giving away the TBR. They're giving them away now.
Edited by AlphaToaster, 29 October 2015 - 12:16 PM.