Horde hunting is probably the best method of hunting with your conditions, since, by seeing 5 Pokémon at once, it offers roughly a 1/619 chance of finding a shiny per battle.
Shiny hunting by hatching eggs is only good when using Masuda Method, or if you really want to use a a shiny competitively. When going up against full odds, it’s one of the worst methods for encounters since it offers a very slow encounter per hour rate. However, there is no other way to hunt Ralts in Gen 7, and the only other way to hunt it in XY is in an area where it has only a 5% encounter rate, so breeding is the best method of hunting in those games.
If you’re hunting on two or three systems at once, the best advice is to just keep doing what you’re doing and be patient. If you only have one system, then only hunt on ORAS using hordes, as that will let you see more Ralts significantly faster.