Well it seems that the actual problem is on your end. Just in case, you can compare your game to these screenshots. They were taken at the places, where you seem to have a problems: slave menu and stat list, slavery guild and all the buttons. Also, I completely disagree about your statement about mods. There is no perfect game, but mods can help you to customize your experience, making gameplay exactly as you want it to be. For example "Gigastructural Engineering" mod for Stellaris adds tons of fun staff to play around with, but it is quite unbalanced and would be a bad idea to include in a vanilla. There are also tons of mods for different games that tend to overhaul them completely, so you could enjoy your old games with a new spark of interest. Anyway, here are your screenshots, hope you will be able to identify your problems and fix them:
