So your change is always zero. is this correct?
Ideally. Yes, as mentioned based on the heuristic used, you can possibly fool certain algorithm which determines the link based on the specific aspect. I imagine you can fool the algorithm if the wallet were to allow the change address to be a different type (bc1 to p2pwkh and vice versa) but it does have a very limited use case, as compared to a mixer which could destroy the link completely, albeit with some fees.
And you mentioned the mixer address. Is this address of some real shuffling service/wallet you use?
Yes. It was discussed earlier. It would be a service or could even be sent to an address which could be used for coinjoin afterward.
Regarding Electrum, it would be much easier to adapt the change there if the fee fixing was allowed before (but not after) building transaction as it is done in Armory.
Well, I'm not sure about Armory but as o_e_l_e_o described, you can replace the amount with ! for which the client would adjust to spend all of the remainder after fees to the mixer.
A big advantage to this method would be the ability to select inputs using Coin control as well.