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 $2500 worth of BTC since the price has dropped.
That actually makes sense to me it you could play the markets they way a tether coin is needed in between. I guess this only csmr into my mind looking at the percent change over 25 hours being up to 7 to 10 points between the worst and best performing coins. My kbowledge tells me you'd have to look at the minute to minute difference as stated above and that's where there is a fraction of a percent change since all coins are more or less tied to eachother.
Back to the free for under 500$ and open source trading bots i guess while I'm unable to trade. I just hate how they all prefer binance and I only trust coinbsse pro where your account requires an SMS for every new login AND 2fa if desired. I lost a whole months trading profits a year ago to some sort of keylogger.