GameCast You're right, It appears Batocera is built more on the Performance side and a little for Visuals, I can live with that. Batocera's default theme is looking good for me though, but I could prefer a more retro look. I had to update joinski that the Zoid Theme does work, placing the theme at "\BATOCERA\share\system\.emulationstation\themes". Wondering if I can edit that to make other themes work over it.
Edit: Looks like I would never be able to do it myself since comparing the themes that work and the ones that didn't is a lot different, or maybe a lot different since not all themes are compatible as what GameCast
said it must be for a RPi3. Moreover, editing HTML's are not my thing. I can stick with the stock theme, zoid theme or wait for a working theme along the way.