I agree that a direct comparison of points is not the best way to compare units. However why do you think an engineer is still a good choice to accompany a mortar? He has to declare which warmachine he's going to help at the start of the shooting phase so either he has better things to do (helblaster) or in the other case, if you get an engineer just for the mortar, you just made your 100pt S2 warmachine 65pts more expensive. Totally not worth it.I don't think using an engineer for a mortar is a good choice, however my point was that each unit needs to be priced in mind of the other units in the army. A ranged unit is a lot more valuable to some armies compared to others.
And buffing the mortar with magic is all nice, but too situational. You have to use most of your power dice to do it, the opponent has to not dispell it, and then you have to hit with your mortar. So, far too random.
The mortar does get better if you start syncing it with other units/magic, however without the buff it still isn't a terrible choice. Yes, it isn't our best option but it is far from a terrible choice. Compared to other 8th pieces, it doesn't price up too bad.
I agree that you have to look at the role a war machine plays in the army, let's compare (only compared with 8th edition):
TK: A lot of weak magic, great BS shooting, below average combat > need strong war machines > skull catapult is the best 8th edition template war machine
O&G: below average magic, bad BS shooting, above average combat, some special tricks (manglers & fanatics) > need average war machines > rock lobber is average
Empire: above average magic, bad BS shooting, weak combat, some special tricks (steam tank, war wagons, good saves) > need strong war machines > cannon is great, hellblaster is average, hellstorm is weak, mortar is weak
VC and Ogre Kingdoms have no war machines, although the Ogres have monsters and chariots that do the same
Conclusion: none of our other war machines comes close to the performance our cannons and yes cannons outperform war machines of other armies, but empire needs more diversity!