The thing is with these sort of grand strategies, especially historical simulations, is that they adhere to limitations of waging war, the AI can't just be made to declare war because it wants war, it also has to adhere to casus belli and such variables in consideration. A lot of games like Civilization for example can be made very aggressive since they're not grand strategies and don't adhere to the same sort of game rules. Though since Stellaris uses a war goal system, it can be more aggressive, but it's still important to consider the goals that must be set and the negotiation process for what is claimed and what treaties are formed, since the AI shouldn't just follow a simple aggressive conquest only approach. The idea of wars in grand strategies aren't about total conquest or extermination, since wars can be used for other strategic reasons. It's much easier to develop an AI that is aggressive and only wants conquest than one that uses war strategically for the outcome of treaties/other stuff from negotiation process for peace.