I'd be very interested to see a few samples, starting from for example 0.002 BTC, taking different routes, and showing the total cost (losses) per step until the final amount that arrives in your wallet.
Here are a couple of quick calculations for Binance:
0.0005 BTC withdrawal fee ($4.22 at current prices)
0.1% trading fee
Cheapest withdrawal fee of a top 20 coin - XLM - 0.01 XLM withdrawal fee ($0.0006 or 0.06 cents at current prices)
A straight withdrawal of 0.002 BTC would give you at 0.0015 in your wallet.
Trading 0.002 BTC to XLM, paying a 0.1% fee, and then a 0.01 XLM withdrawal fee, would give you (at current prices of 731 sat per XLM) 273.3142134 XLM.
If you were then to use CoinPlaza (for example) to swap from this XLM to BTC, you would be left with 0.001998 BTC.
Doing the same calculation for the next cheapest withdrawal - XMR - 0.0001 XMR withdrawal fee ($0.005 or 0.5 cents at current prices).
0.002 BTC on the exchange would become 0.31268178 XMR in your wallet.
Using CoinPlaza to swap would give you 0.001975 BTC.
So for small volumes, it seems much better to withdrawal in a coin that isn't BTC. Obviously once you start getting towards larger volumes, the 0.1% trading fee becomes that much larger and quickly dwarfs the amount you would pay on the static withdrawal fee. Given that the XLM withdrawal fee is so small in terms of fiat, the difference between the BTC withdrawal fee and the XLM withdrawal fee essentially becomes the BTC withdrawal fee. So once the 0.1% trading fee becomes larger than the BTC withdrawal fee, then it makes more sense to just withdraw in BTC. This would be reached when trading 0.5 BTC or more.
This obviously doesn't take in to account the fact that the price may fluctuate in the time it takes you to do all this, the extra risk you are exposing yourself to by using another third party service, and the extra transaction fee to send your coins from your wallet to the third party exchange service. And again, it goes without saying that when an exchange is charging you 50,000 sats for a transaction which costs them ~300-400 sats to perform, they are ripping you off.