sub 1 cent usually

If you're tipping someone less than that you're quite the scrooge 😂 

 Damn, Bitcoiners are cheap for being so rich 

 Good point 😂 

 Being private AND offchain is definitely ideal for privacy. That is true.
Monero gets L2s with FCMP++ in a year or so.

"There is no reason to use a different monetary token & deal with exchange costs & risks & lack of acceptance."

What? You deal with exchange costs and risks in lightning, liquid, and ecash too. You also deal with the additional cost of force closure fees in lightning, and rug risk with ecash. Liquid rug is also possible too just much less likely (privacy sucks though. doesn't hide sender/receiver and abysmal anon set).

https://boltz.exchange/ 

 As vossas opiniões são uma shitcoin 

 Yea you have to do it properly
Swap back to Bitcoin broken into different amounts and at different times. Don't consolidate after.

-Cashu: Strong choice if you don't care about custodians for larger amounts sure. I would be worried about anon set of the mint though.
-Lightning: Maybe could be decent choice if you dont mind dealing with complexities and painful UX (you don't get the full privacy possible on lightning without running your own node. Custodians and LSPs sacrifice at least some privacy).
-Coinjoining: I wouldnt consider as a strong substitute since it is not only weaker obfuscation (nothing is hidden via encryption like the other options) it is also recorded on chain.

"If so, why not just use those instead of abstracting farther away from your SOV asset?"
Doesn't SoV imply long term? Swapping would be short term stuff. It shouldn't significantly affect the price at all. You could even make a tiny profit at these time scales from swapping. 

 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. 

 I guess it's a matter of risk preference. Risk being rugged by 
custodians, or risk slippage in price. 

You might never be rugged. 
Or maybe you get rugged and instead of losing 5% from using Monero,  you lost 100% from being rugged.

Up to the person to decide, but I don't think there is a risk-free or cost-free option. You pay in time/money/hassle