The "you have to do it properly" is kind of where things start to break down for me. The alleged benefits of privacy by default break down once you realize that people don't have an economic incentive to stay in Monero, for various reasons. You can clearly see that now. So we are right back to not having privacy by default since people are expected to do things a certain way. I'd rather just have Bitcoin bound tools for people to use if they want to that doesn't require them to use an entirely different currency that they may or may not be able to get in or out of when they want to. 

 The "you have to do it properly" part also applies to moving BTC thru Cashu, Lightning, and Coinjoins as well not just Monero...

The major problems arise from Bitcoin on-chain itself being transparent

Cashu and Lightning are functionally different currencies and don't inherit on-chain network affects. I can't send on-chain Bitcoin to your lightning invoice. I have to get sats on the lightning network first somehow. Just because a merchant accepts on-chain Bitcoin doesn't mean they accept Cashu or Lightning. It's very likely that they dont.