It's bad on every map. It has the same weaknesses, but each map style accentuates some of them.
A linear map like Road to Kharkov means scouting its construction and anticipating its placement will be easier, while indirect fire can be concentrated without inconvenience alone or with a forward HQ/reinforce halftrack to destroy it. A wide map like Moscow Outskirts means it can't keep up support of your forces properly and will be vulnerable to a direct attack if you don't blob around it thus tying your units down. A balanced map merely makes both apply equally rather than accentuating one.
The mortar pit is something you build not because you want to but because you have no other choice. And the advanced emplacement doctrine probably makes people assume it's better than it actually is.
1-Not true. It's AWESOME on small choke point map style. While a mortar pit has vulnerabilities on 1v1, it's not the same on 2v2+
2-If you let a mortar pit set down, it's a pain in the ass if you don't deal with it quickly.
3-On Moscow it may not be ideal to get one early on, but on either bot or top spawn near mid or behind hedge, it can provide enough support for the whole mid fight.
4-Any commander with stand fast also proves annoying to deal with. Cancer commanders makes you unable to deal with them on small maps using indirect fire at all.
All right. Point being though that the increased range of the mortar pit is a necessity and not a bonus, as other mortars can simply move to adjust their range.
Obviously that the range is a necessity since it's immobile. What some people argue is it's "afk" nature or lack of player input when using them.
Reduce autoattack range to 80/100 but give it's barrage a shorter duration and almost no cooldown. I'll say you could give it a secondary barrage with lower damage but a bit higher range as well.