Since you can´t totally switch off the planetary AI, development plans and the empire settings are the only thing to keep control of that.
You can only have so many dev plans, thus you need to create them in a way that at least one applies to every planet you own. I for example have 3 types of dev plans:
1. Frontier, Secondary, Primary, Core: distribution of planet defense, military and production appropriatly
2. Red ring, yellow ring, green ring: setting of terraforming importance, possible farming as well
3. Specialized: e.g. mineral rich, high biodiversity = mining and farming priorities
I also use the all planets option. I have only shortly used the user defined planet categories, yet they prove useful if you want to specially control certain planets.
In the Empire tab I still use the natural setting and that didn´t make that much of a difference to specialized. In the beginning you should definitely use natural, as this setting ensures that the planet AI builds DEAs where you are short of resources. Only later in the game a specialized setting might make sense.
The only other way than using dev plans is either to let your viceroys decide on their own, they will then solely rely on the empire setting. It works, yet of course it´s not as effective.
The other option is to check each planet every other turn and select the DEAs yourself. Yet since you don´t have any control over the additional buildings for the DEAs, this is not adviseable.
You need to experiment with the dev plans and put them to best use. And you can concentrate on a few planets yourself, to maximise the efficiency there. But be aware, the really effective planets in the beginning will most likely just be mediocre in the end of the game.
