First have a proper discussion with your diabetologist. 'Poor control' to the CAA is different from 'poor control' to doctors.
Then discuss the various oral medication that is allowed and why / if insulin is better - it may be simply a particular protocol the doctor is following
If insulin is the only option, you have to be given the consequences of not taking it. Do you have any end organ complications - eyes, kidneys? Is this a potential risk for the future???
The 'allowed' drugs such as metformin do not actually lower blood sugar, they stop it rising. So they are unlikely to create a hypo. That is why you can keep flying on them - you wont become incapacitated. Insulin can produce a hypo, needs to be closely regulated, and needs adjusting in the early months. Even the enlightened CAA will not let you fly until you are stabilised on a regime and have demonstrated your blood sugars are controlled.
I am to be convinced that the benefits in a typical type 2 are justified against these difficulties for your flying BUT only your diabetologist can give you chapter and verse - we merely provide general information and I cannot advise you specifically without all your data
As always, we love to hear the outcome!