let me put it in simple terms w/o numbers.
you're taking a chunk of coin off a very secure ledger and moving them over to a less secure ledger. it's too be expected those coins moved will be worth less b/c they are now less secure.
b/c of arbitrage, you can expect the moved coin to drag down the price of the not moved coin to a lower equilibrium.
If I'll move my BTC to SC then no one is able to arbitrage them. Only I have pk. If I'm so stupid and sell them for less than is bitcoin price then arb boot can do profit. It is up to you if you sell for less (in panic) or convert back into bitcoin.