The "accounting model" is even easier to trace, I'm not sure what you mean by that. For example, here are all USDT transactions: https://etherscan.io/token/0xdac17f958d2ee523a2206206994597c...
For Bitcoin these are UTXOs which are easy to trace, but not so for Ethereum and its tokens which just rely on accounting not UTXOs. Right?
No.
> Let's say I send you $100 USDT and Osama Bin Laden sends you $100 USDT. Then you send Justin Beiber $100 USDT and keep the remaining $100 USDT.
That's a misconception, you can do that exact same thing with Bitcoin and you are left with the same question. Bitcoin outputs can be combined into a single output (and they routinely are). See this diagram: http://syskall.com/bitcoin-notes/svg/transaction.svg
Even Ethereum's rationale acknowledges that Bitcoin's UTXO model provides a higher degree of privacy: https://eth.wiki/fundamentals/design-rationale