I have the same feeling about all of this, and that's why I never bother exchanging my BTC to some fast alts in order to make a fast and cheap transaction. However, it would be interesting to see the real numbers. I bet you will lose more money in the process compared to just sending BTC and paying the highest reasonable transaction fee, like 40k+ sats currently, but it would be interesting to see the following calculations.
Say, someone buys $500 worth of ETH with his BTC. Sends ETH to wherever he wants. Exchanges ETH for BTC there. How much this person will really lose in the process? I assume, it can be more than $5, but I don't know how much exactly.
Depends on the exchange if they're using a popular exchange like Binance for converting it's usually more than spending a recommended miner fee for Bitcoin because of the fixed withdrawal fee. Apart from the additional miner fee from the deposit if $500 worth of BTC is
BTC0.06 then Binance is charging like 0.1% on trading fees there's a
BTC.0006 trading fee(plus the fix eth fee) total estimated cost is $15 after conversion. This is assuming the price of ETH is stable, the cost or loss in value could be greater as the rates from exchanges are different.