Alliances are much more useful than you make them out to be. Apart from the mods, getting allied faction units for good boy points is a way of quickly growing your army since they spawn instantly inside your main city, ignoring any production queues, and I often ended up in situations where I had good boy points to spare, since they're just another resource you "harvest" and there are structures on the map and society upgrades that increase your good boy point income. It's even more useful if your faction or tech has upgrades that synergize with the allied units. For example, imperial spearmen are very good if you have energy weapon tech, so you can give them shit like static shields and then use them as a melee tank stunbots. Forsaken/forgotten (I forgot what they're called) have those tanky little golems that shoot entropy bolts and can be used as an AoE artillery, that I often get no matter who I'm playing as, and they're even better if you have entropy damage tech. I was often in situations where I could buy 2-3 tier 3 allied units before I could even research tier 3 units of my own faction, which is a pretty big power spike. Would be nice to at least have the option to capture neutral cities and build their units normally, but I already said that I also think that this system could have been implemented much better.