After purchasing Season Pass, we still must purchase DB BR 101 and DB BR 406 for the Riesa-Dresden to run properly. If this is true, then there is no discount. We should be getting routes ready to run. Please explain!
The route will run absolutely fine without them (minus those services). I believe the 406 is the one that comes with Koln Aachen, so we all have it anyway. That leaves the BR101 (for which you would need HRR (its home route) and the 101). If you desire to drive the 101 on Reisa, you will need those two DLC's - however the Reisa Dresden DLC would be entirely playable (with the exception of the 101 services) without the 101.
It's a layer, not a dependency. Big difference. The 101 layer is for people who own it. If you don't have the 101 (+HRR) you still can drive all the locos on Dresden-Riesa that are in the timetable. So the route IS "ready to run" - just not with the 101 as long as you don't own it. And infact you do own the 406 already, so that's good to go.
It is not a Season Pack. It is the Rush Hour Ticket, and it gives you exactly what it says: The 3 Rush Hour routes. It does not include other DLCs released previously.
Think of the BR101 services as an extra freebee for those who already own it, rather than as a dependency for those who don't. While, yes, it does mean if you want BR101 services on Reisa, you'll have to buy it and Hauptstreke Rhein Ruhr, Reisa will run perfectly fine without it. Same goes for most German routes, actually, as well as some British routes now (a railtour enabled though ownership of the Northern TransPennine route seems to becoming standard).