I think I understand what you're trying to say. You have ETH and BTC that is worth roughly the same amount and there happens to be a same level of percentage increase I'm both markets,  and you sell ETH  for BTC and market drops back to what it was before, would have loss or profit?  I think you still have what you had before. Unless you exchanged it for a stable coin and market returns to what it was before the increase, you will still have that same amount and you can then decide to buy the $2500 worth of BTC since the price has dropped.