I’ll try to help from a purely persuasion perspective.
If people are apathetic or against any idea, facts aren’t usually going to persuade them. Facts tend to be the least persuasive route to changing attitudes. I imagine forming your team is loaded with so many associations and connotations. Are people losing resources or dignity by having a smaller team etc? Are you moving into or out of someone else’s turf? Is it more or less work for others?
Persuasion is pretty simple to break down. There’s the cognitive, behavioral and emotive component. It combines what people think about the idea, their experiences with the idea, and how they feel about the idea.
So I’d find some very emotive stories about why forming your team is important. Find out how people like them decided to let a team below them flourish. Talk about the talent in your team that are feeling suffocated. Identify some of the core emotions that you could build a good (short) story around.
Then look at the behavioral side. People don’t like the new and unknown, so how can you shrink that behavioral change initially? Instead of forming your own team, could you have a little more autonomy first? Could you begin acting like the team does exist and reporting your own metrics for the group’s success. Can you name the team? Make the initial behavior change as easy and as simple to perform as possible.
Then the cognitive side is finding new information that they can accept. So if they are against starting a new team, identifying information which makes forming a new team sound like something they would do. I.e. the tradition of not having messy organisation structures or whatever
That’s probably a rough idea of the persuasion angle. Less about facts, more about emotions.
Aside, if you need more investment, then there might be a more direct route with the decision maker. But I’d begin building that relationship very early.