If a state does not allow non-residents any mode of carry, does that not effectively create a ban?
I don't see how, in legal terms, although it does in practical terms.
Basically, one is not forced to travel to any other state. Unless you are required to, by law travel to another state, ALL travel is voluntary. The fact that you may need to go, on business, or for any other personal reason is a matter of personal choice.
And since it is your personal choice, you are not being denied anything by the law. You are choosing to go there, and by doing so, give implied consent to abide by their laws while there.
It is your responsibility to determine what, if any difference in the laws exist, between where you are going and where you live.
That a lawyer does not do this before traveling, and considering the simple fact that NYC has had uber restictive handgun laws for generations, shows a lack of forsight. This does not reflect well on his capacities as legal council, in my opinion.