The "problem" with mortars in darkest hour when you are playing public is that the mortar dies and lives with the guy who plays the observer. If you have somebody that just picked the observer because the class is not called Riflemen and is not willing to mark anything you have a problem.
Well, that happens in DA too some times. THen you have to accept the fact. Just like you get an crap sniper that cant take out MGs and other sniper and just runs in as close combat.
WHat you do then is to move up closer and get eyecontact, or have an friend to get closer to the target and just tell you how much you have to adjust
"more left, more right, further, closer.. DEAD ON! FIRE FIRE FIRE"
IT works wonders, harder than with an good observer but it works.
It can easily be worked around. And if you just give the artillery observer some crap equipment ppl wont use it unless they are spotting

Say, a pistol and binoculars or so. No main weapon, who would want to rush into combat with that when you can have a 98k or Nagant + 2 handgranades?
And again its the same with the SL, if you have an crap SL who just grabs it because they want the G41 or STG44.. Its the same, you work around it but atlest then(with mortar) you have a snowballs chanse in hell to actually get some rounds into the enemy target.