I get the impression that the timetable is missing a lot of other services - for instance you can sometimes get held at a red for no apparent reason or switched from Slow to Fast lines and back again in what looks for all the world like an overtaking manoeuvre only there is no train to overtake.
This is on Great Western Express, probably?
The dispatcher optimises the route based on distance, it can sometimes happen that slow->fast->slow is a few yards shorter than remaining on the slow line all the way through. At that time that route was built, DTG did not have the tools to visualise which route a train would take - the only way to find out which route a train takes is to drive it all the way.
some of the scenarios are ludicrous. Such as catch a train into Paddington to then drive an HST to Reading. 10 minutes watching the scenery pass by. Then 15 minutes sat doing literally nothing waiting for the HST departure time.
Some of the scenarios work better if you see them as tutorials. The 10 minutes of "watching the scenery pass by" is to introduce you to the passenger aspect of service mode: just board a train and sit down.
They need to make more routes and trains and design some decent scenarios to make TSW more attractive IMO.
They are working on this, but it takes time. DTG aren't the biggest of companies, while route building for UE4 is a time and labour intensive process. It's not a mainstream game either, it's not like they're building the next FIFA or Battlefield
DTG recently announced the next route: Darlington - Saltburn-by-the-Sea set in 1989. This route comes with a Class 08, Class 37, and 3-car Class 101 and seems to be mainly focused on freight traffic in that area.
They're also still working on releasing editing tools and guidance, once these are out it'll become possible for people to make their own routes, trains and scenarios. How those will be distributed isn't known yet though, getting community content to consoles is rather hard as it'd involve Sony and Microsoft.