But should we say that BTC without mixer aren't anonymous?
no.
bitcoin anonymity has nothing to do with mixers.
you can be totally anonymous as long as the bitcoins in your address is not linked to you personally.
for example you can buy bitcoin with cash and receive it in your bitcoin address, that way nobody can know this address is for "you"
But you could trace
BTC at everytime on blockchain and it's really difficult to buy large amount of
BTC per cash in a lot of country
yeah it can be traced and yeah it is hard to buy large amount of bitcoin with cash, but my point is something else.
take this scenario as an example for 100% anonymity.
you meet someone face to face and pay him cash and he sends
BTC to your address lets call it address1 and you use that
BTC to pay for a service to address2, lets say you buy a VPN with your
BTC now anybody who is tracing the transactions sees bitcoin coming in address1 from some source and goes out to address2 the only thing he can get out of his trace is (with a low chance) the owner of address2 and sees the funds were spent to buy a VPN.
and in all this your identity was never revealed.