Yes, since EaW was build to have those kinds of maps whereas Sins was not. Sins is essentially designed to have randomized templates distributed, so the system to place objects specifically can be a little more cumbersome.
For example, for EaW, this is what it looks like (I'll just use an example where Yaga Minor is the only planet. In EaW, Yaga Minor is its own defined entry. You then reference that entity in each GC in which you want to use it.
<Locations>
Yaga_Minor
</Locations>
Then, to have that planet controlled by something, it just looks like this:
<Starting_Forces> Pentastar, Yaga_Minor, IPV </Starting_Forces>
So you just drop a few of those in like that, and the forces spawn as you see in EaW.
For Sins, it's a bit different. Planets, instead of being externally referenced entities, are created within the scenario file (which makes sense, because Sins allos for a lot more randomization and is not built off the idea of a specific universe ie Star Wars). It looks like this:
planet
designName "Planet70"
inGameName "Generis"
type "Mountainous"
pos [ 726 , 259 ]
moveAreaRadius 40000.000000
hyperspaceExitRadius 30000.000000
owner ""
isHomePlanet FALSE
normalStartUpgradeLevelForPopulation 3
normalStartUpgradeLevelForCivilianModules 1
normalStartUpgradeLevelForTacticalModules 0
normalStartUpgradeLevelForArtifacts 10
normalStartUpgradeLevelForInfrastructure 2
quickStartUpgradeLevelForPopulation 4
quickStartUpgradeLevelForCivilianModules 1
quickStartUpgradeLevelForTacticalModules 0
quickStartUpgradeLevelForArtifacts 10
quickStartUpgradeLevelForInfrastructure 2
planetItems
templateName ""
subTemplates 0
groups 0
spawnProbability 1.000000
useDefaultTemplate TRUE
entityCount 0
asteroidCount 0
Normally, you'd put TRUE for ishomeplanet and then, a bunch of those would act as home planets, randomly spawning in factions as required from player setup. Then were the templateNAme and groups are you'd set up a bunch of spawn criteria for things. For a pre-set scenario, you need to set it up so that each player coincides with a specific faction, and it forces each player slot into a specific faction in addition to setting up all the forces. In EaW, if you select a different faction, it loads a different scenario file (fun fact: ach version of a given GC is actually coded once per playable faction, even though they're almost always identical). Sins does not have pre-set faction requirements, so if you choose New Republic on a map, it's still just going to reandomize you into any given slot if you let it. This means each scenario has to be coded once per faction as well, but in Sins the player will have to select the proper version from the scenario list (they don't group like how EaW does).
It's still possible, and in general the Sins version offers a ton of different options in terms of combustibility and replayability, however it makes preset scenarios kind of annoying to make.