You SHOULD be completely fine if you follow the strategy the tutorial messages suggest, but there are many other ways to go about it. While it would be optimal if you followed the common strategies of the 10/10-destroyers (for example Kahuna and FaultyLogic have left many pieces of advice in these forums), you should experiment as much as possible and find whichever playstyle you're most comfortable with.
Back then I solved the final tutorial according to my own (very bad) playstyle: Basically being the Spire Empire and slowly rolling over everything.
Taking over literally all systems in the entire galaxy (one "chunk" at a time or one by one, depending on how strong I am), setting up impenetrable defenses on one chokepoint after the other until it was next to the AI Homeworld and then building ALL units up to cap and FRD-sending them into the Homeworld (only manually controlling a small group of ships which are good at taking out guardposts while the AI's mobile defenses are being decimated by the FRD'd fleet).
I'm definitely a bad example and you shouldn't follow this strategy (AI War is generally played as a guerilla war where you try to only take territory you HAVE to take) but it CAN score wins against 7.3/7.3 and even 8/8 AI opponents (I have done so on 40, 60 and 80 size galaxies and have been working on 120 size maps for a while, it's challenging but also very entertaining to play this way when AI progress nears 1000 before you even arrive at the first AI homeworld).
I can't even remember which strategy game made me get used to playing like this, but I've been that way ever since I can remember (all the way back to SC:BW, WCIII and Age of Empires). I just don't like having many frontiers and having to rely on mobile defenses or the pathing of enemy waves.
Anyway, I hope you get to enjoy the game as much as possible after getting through the tutorial.
It's very entertaining to get crushed by this amazing AI and very fulfilling to succeed against it (it's the Dark Souls of Grand Strategy games, or is Dark Souls the AI War of RPGs?).