Indirect fire does affects all teams, but I think ost is hit most by it. All the other factions (possibly except brits) have mobile mainline infantry (double bars, STGs, PPSHs, etc.); Ost/Brits NEED to remain static to be effective. I think the problem affects ost the most, though, simply due to the smaller model counts.
trust me, ost is the LEAST affected since they only have 4 man squads.
what happens is that a mortar hit dead center a squad and you lose 80~90% of the squad health on the first engagement and now you have a useless squad for the next 3-4 minutes until you get healing.
and being mobile means nothing since mortars have laser guided technology that hit squads on the move.
The older model was much better, sure you would get wiped once or twice, but it was very rare when you microed good, now there is nothing you can do since mortars are basically rifles nades that get fired for free.