Have you seen the smoke land next to you from an opponent mortar user? Maybe mine was bugged, but it's a small puff smoke good for nothing. It's not like a smoke grenade.
Making the mortar stronger but harder to resupply sounds like fun. I can imagine setting it up temporarily with special purpose rounds as part of playing the objective. At the moment the player tends to sit in a safe position on the mortar forever, making it not really a gadget but an entire class of its own.
The mortar currently is more suitable for the defenders in Breakthrough to use because it can be set up far behind the defensive lines. I was disappointed and amused to see the difficulty an attacker would have trying to use the mortar to soften the opponent's defences on some maps like Empire State Breakthrough, where the opponents roam around the edges of the attacker's HQ. Even on Sobek City, trying to target the defenders on the rooftop was impractical because you have to set up in a vulnerable area too close to the action. This would not be as much of a problem if the mortar was a shorter-use and more powerful gadget to use on the way to the objective.