As a T1, I don't expect my GP to be very clued up on my insulin needs, so I can understand your frustration with the rarer T3c, which has its own unique challenges, given that the pancreas does a lot more than just produce insulin.
I would argue that it's more similar to T1 than T2 because it generally results in lack of insulin, but if your pancreas is still producing some insulin maybe T2 dietary techniques can be used to help make the most of however much insulin you have??? And of course, there is a big difference between a damaged pancreas with limited insulin production and a person who's had a pancreatectomy and has no insulin at all. And as a T1 my pancreas still produces glucagon which helps me out with hypos, whereas someone without a pancreas doesn't produce it. (And that's ignoring all the other enzymes produced by a pancreas).
And unfortunately the rarer your condition is the less likely it is that non specialist medical professionals will know about it. I suspect that your best bet is to just keep educating the people you meet about it.
Should it be treated differently to T1 and T2? I'd argue yes, but only people such as yourself can say whether that is happening in practice.
Depending on the amount of damage to the pancreas it can be treated more like T2 or more like T1, both are fine as long as they work.
An important difference between the treatment of T3C and other types of diabetes is that with T3C it's often needed to supplement enzymes for digestion (creon). In T1 and 2 the production of those enzymes isn't affected, but in T3C often it is.