The general rationale of Heller is that a "long standing" condition becomes constitutional. That sleight of hand was employed to preserve the GCA of 1968 and similar federal restrictions on the right to keep and bear arms.
I agree with you - that same rationale can be used to uphold long-standing limitations on issuance of "bear outside of the home" conditions. Just hold that non-uniformity in this regard is to be expected, and the question is a political one, not a matter of personal right that the courts will recognize.
The courts are hostile to the right to keep and bear arms. They would not take this case if the intention was to allow more people to bear arms in public. Several circuis have already weight in, that way. SCOTUS will choose among them for the rationale. Decision is made before the case is heard.
Past due time to return that attitude in kind.