I'm sorry, but your current method is one, which is known to behave like so.
I don't want to block your suggestion, but I think I know the reason, why you are suggesting that and can tell you how to avoid that.
The distinction between station A and B is useless, because you cannot distinct, if a barrel belongs to a station. If that would be possible you have different barrels which cannot fit into one stack. And they needs to be counted as different items, and the consequence would be to have as many different types of barrels as outpost stations... Well in Germany we have those systems for empty bottles too, and have mixed systems with bottles, where it doesn't matter where I bring it and other bottles, which needs to be delivered at some special brewery only. Why not? It's eventually a good idea!
But my example with the empty beer bottles shows the problem: you need to create different barrels, to distinct that in a way, which can be handled over all instances. I think this is no option yet. Or only an option for a mod.
In my opinion
you need to think for the empty barrels as an endless resource. Then you will see, that it sooner or later will happen, that the empty barrels can block everything, no matter how you are doing it.
There are generally two or three ways to avoid that. In all cases you need to
limit the number of empty barrels with smart inserters.
1. Use two wagons per train: one for the empty and one for the full barrels. You need of course to built the train stations like so, that the trains always have the same direction that the train cannot turn into the wrong direction somewhere. At the target station you can use smart inserters to unload only the needed number of barrels (logistic network). But this isn't really needed, if the layout avoids mixing the flow of the barrels. I would call this model also a transport-network-model, because you can built it with simple chests, simple inserters and transport belts only. This model might also fit the best way in your current setup.
2. Use one train for the empty and one for the full barrels. Like in 1) the empty barrels are unloaded at the target station only, if needed there. This model works also with the simple transport, because you can built it up like you have transport belts only. At first it looks a bit like waste to have two trains for this task, but if you connect your railway systems, this train can deliver all outposts with empty barrels, and the train to fetch up the full barrels does it also. The biggest disadvantage is, that you need always 2 stations: one for load and one for unload.
3. This can be optimized a bit, to use only one station for load/unload. You need only one train per target. Train is loaded with empty barrels only, if they are needed at the target station. You need a long smart wire for that and need to connect all storage, requester and provider chests at the target station to that wire. In the base station you fill with the smart inserters only if some barrels needed. At the target station you have on one side of the station the unloading of the empty barrels and on the other the filling. Also at the main-base station. For this model logistic bots and the usage of storage chests is recommended!
4. I use a combination of 2 and 3: one train per transport direction and one station for load and unload only, so I have in minimum 2 trains and 4 train stations. The reason is, that I want to use the train also for other stuffto bring into the outpost, like repair packs, ammunition, stuff. And for the returning train I want it to be loaded also with ores, coal and alien eggs. You can have a look at
https://forums.factorio.com/forum/vie ... 8&start=10 to have a view at this.
5. To avoid the long, long wire you can use also the method found here:
https://forums.factorio.com/forum/vie ... 687#p22686
This is a nice compromise.
So in conclusion I would say, your suggestion is logical, but we as players need to use first all of the other methods for a longer time before we can be sure that we need something like your suggestion.