Requiring users to learn the idiomatic way your software behaves in order to be productive may be warranted if your functionality is complex, heavily used and more or less unlike any existing software.
Or, your software is niche and its alternatives have such terrible UI that trying to do what the user expects is adding 3x clicks and actively hurting their productivity.
There can be legitimate cases for learning curve, especially if unlearning is involved. If so, the fact that your designer wants the user to learn is a very welcome position. If they make learning effortless and intuitive, you may end up with a solid piece of software.
Or, your software is niche and its alternatives have such terrible UI that trying to do what the user expects is adding 3x clicks and actively hurting their productivity.
There can be legitimate cases for learning curve, especially if unlearning is involved. If so, the fact that your designer wants the user to learn is a very welcome position. If they make learning effortless and intuitive, you may end up with a solid piece of software.