Ostruppen are very much viable at least in 1v1s if you are good with snipers and HMGs. They are the meat shield for your MGs and with fausts they can defend your sniper from light vehicle rushes. In cover and long range they can trade MP with allied infantry. They don't really bleed MP so you can more easily get big army.
Muni convert and railway seem to be a waste in that doctrine imo. If you go ostruppen you have a lot of freedom with your muni purchases, you can get flamer and med bunker early and plant all the mines you need. And railway is just large area denial and you never get any kills with it unless your enemy falls asleep, but for area denial it's way too expenive if you compare it to incediary barrage.
I'm not a 1v1 player by any margin so I can't really comment on there viability there. But in 2's the amount of DPS and MG's on the field tend to make Oustruppen hard to use because they don't have any real "umph" to them.
Tbh the best thing IN Oustruppen Doctrine for me is the fuel to muni conversion because I can spam mines, LMG's and shreks and railway enemy bases at the end just as a big "fuck you" for letting me get to 12 CP.
I really like the concept of Oustruppen, but the doctrine is anemic due to the ROF bonus being bugged in buildings and trenches being very underwhelming (good for cheese like blocking retreat paths tho). Something like a Command Tank to reduce damage or increase damage on top of the synergy with the Artillery Officer would go a long way towards making it more interesting.