>>28597496You'd expect that, but my experience has been different. (For that matter, the maths says even if you have only 4 basics in your deck, you still have a 40% chance of not needing a single mulligan, but it can be deceptive because of how high the chance of requiring multiple mulligans is.)
I'm running this deck right now (hi again) and I never really have any issues with my opponent getting too much advantage from the mulligans. The Red Card also really helps, since if I'm the starting player I can usually sift to it or Skyla (and then use the Skyla to search for it) and not only negate the mulligan advantage but often also reduce their hand (often enough even without mulligans they stay at a >4 card hand after setup). In an earlier build I also used N both for this and for its normal purpose, but N being a supporter really limited its usefulness.
(Before you ask, the Birches are an intentional replacement and I *did* have four Sycamores, but I found myself losing too often for emptying out my deck too quickly.)