I think this is unfortunately true. I didn't realize until I opened the scenario in the editor but your enemy actually starts the battle one or two hundred kph faster than you, which is enough of an energy advantage that even a spitfire might be able to catch up to you. To make matters worse you're barely above tree top height, so no power-diving away. Basically you're in a situation where it's impossible to fly the dora its strengths, at least at first. Understanding this I've been able to get better at the scenario. Your first priority is to extended enough that you can begin to fight on your own terms, or at least prevent the enemy from exploiting their massive energy advantage. It also doesn't help that the AI, despite all the improvements, still does not seem to do particularly well with the D9, so chances are you're going to get outnumbered pretty fast.
It's definitely a winnable scenario, but it is a hard scenario. Probably about the most demoralizing intro to fighting in the Dora I could imagine. It's been a learning experience though. I've found it helpful to get in the mindset of thinking of maneuvers in terms of the space they need to be successful. People always say "stay fast" and "boom and zoom" and that's all true, but you have to understand what that means. You can turn as much as you want if you give yourself room to execute the maneuver without pulling hard into the turn. If you're flying this way it's really easy to stay fast because you're keeping the Gs low, which in turn makes you a less appealing target.