I personally find there's no depth to it: the winning strategy is to focus on growing your economic base and pump all spare capacity into research - by mid-game, you'll out-earn and out-tech every opponent other than the fallen empires.

In my last long playthrough, the second half of the game was literally me just racing against the victory condition clock to see how much megastructures I can cram in, so I can see what they do in a single game. It got briefly interesting for a moment, when a fallen empire decided to start their crusade at my doorstep - I had to engage in some micro-heavy delaying action for some of in-game years, until my exponential trajectory made me out-tech them and I could get back to building megastructures.

I mean, I like the game - but I wish there was some more meaning attached to things, for the actions to be more complex than scaling some numerical modifiers, for the tech tree to not be a tree and not be shared, for battles to be something more than "weapons are rock-paper-scissors, whoever brings more total points into the fight wins"...