Adding to the discussion, a big factor here are their respective play-styles. I don't remember which week exactly, but in an interview with Keith (and from watching some of their games), Keith is a much more supportive carry, where Piglet is more of the "star-player-put-the-team-on-his-back" carry. A more supportive carry will generally play safer and try to get his team fed, where the alternative approach would be to play riskier to snowball extremely hard.
Another example of this would be season 2 (early season 3) doublelift, where he would solo carry games. This is comparable to Piglet's styles. Although if he gets rolling, he'll take control of the game and dominate (no pun intended), if he's camped, well we know how that goes.
And obviously the language barrier is a factor, but I feel like team synergy, in terms of play-style, is the big issue here.
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