Sounds like bitcoin and monero are useless if neither one can't serve both functions. Oh wait... One does.
Discussion
Bitcoin being pseudonymous can’t do what monero does, which is provide complete secrecy of transaction details. Bitcoin was never designed to do this, but monero will *never* see the gains that bitcoin will, so it makes little sense to hold your stack in monero. But if you want your purchases truly untraceable from your KYC-bought coin, hodl bitcoin, then either: bitcoin—>monero—>spend. Or: bitcoin—>monero—>bitcoin—>spend.
There's also options to route your BTC and XMR through Tor and/or I2P, which is better than nothing IMO.