I tried to play this game once and sucked at it. There are people out there who are legitimately good at this, and that's awesome to see for an open source game
I know what you mean, biggest gripe I have with this game is how important it is to play the meta and boom early if you want to win at anything other than easy mode.
I've played perhaps tens of hours of 0AD. I boom early, try to create an unbeatable army, and then go win. When I saw competitive 0AD players on YouTube, they played completely differently: they train cavalry or cavalry archers and go hassle the booming opponents really early. Then retreat to go hunt some chickens for a bit, train some more cavalry, and go raiding again. They simultaneously attacked each other, all the while trying to continually improve their economy meanwhile. It seemed much more fun than the way I played tbh.
The best players are incredible at microing (although horse rushs are just one of multiple strategies). It's also equally important to manage resources and units in a way that you use all of them all the time. That's especially important in early game.
I started playing not so long ago. Here's some good lists of tips that helped me. Although I had some headstart with SC2 experience :)