What is this unicorn you speak of...? :) jk, I know some exist, I've just been irrationally faithful to a bank that probably does not deserve it anymore (coop)...
(But I keep my savings in an account that offsets against my mortgage, so I'm effectively getting a similar deal in practice by not accruing interest on that.)
You can be dinged both for having credit and not using it in a given month, as well as exceeding a certain threshold (~10%?) of your credit limit.
So yeah, I don't think I care too much about my credit rating at all, it doesn't seem to be affected by this in the sligtest.
Also worth noting Credit Karma uses TransUnion which is only one of the big three rating agencies, and arguably the least important compared to Equifax and Experian.