Yes, mortars and late game artillery are two entirely different pair of shoes.
If you are under 152mm, Katjuscha, B4 or Priest fire lategame, an Ostheer mortar won´t help you winning the game at all.
Neither will the current Panzerwerfer.
The (late) artillery game always goes to the Soviet player.
With the Stuka I find that advantage is at least even, and the LefH really isn't as bad as people make it out to be; Allies have a harder time countering it than Axis and it is decently strong.
I'd be interested to see T3 Panzerwerfer, I feel getting it out early would be really risky instead of a normal tank as most people still have their M5's/Stuarts to sneak and kill it.
I just don't get it often enough in T4 to judge it's performance. If I have T4 up then Panthers are swallowing my popcap.