I also have a suggestion for a Legendary Artillery weapon, though it is kinda childish but the idea is unique

Name: Cloud Mortar

Available variants: 8, 12 and 16 energy (Dev choice)

Damage: At base level, for the 8. 12 and 16 variants (all having 12 magazine) deals an approx. damage of 68k, 81k and 104k damage per magazine respectively

Reload speed: due to the relatively low damage capacity of this weapon, it reloads at 8s

Range: has an effective firing range of 30-225m

Perk: Once it hits enemies, applies the "Soak" effect to them, which will reduce the damage of by 25% (can be increased up to 60% with implants) and reduces the speed of hit targets by 40% (damage reduction and speed reduction cannot be stacked if multiple Cloud Mortars fire at the same opponent). The zone it hits will remain "Soaked" for 2s, so if any ememy passes throgh the zone, their speed will be reduced by 20%. For easier identification of the soaked zone, the area it hits will be faintly glowing in a light blue colour

Usage: Can be used to restrict enemies and help allies survive by "Soak" effect. Also, reducing speed of the enemy will help ur allies to capture beacons while the enemy struggles to move/retaliate. Also, you can fire the weapon to block certain pathways using the "Soaked Zone"  

Here is an idea in general for artillery weapons, existing and new. Typically when artillery strikes it strikes an area, field teams send in coordinates, and the cannon operator translates that into the angle at which to shoot (or computers probably do that nowadays) - what they don't do is say "shoot that guy". This is exactly how it works in MA, you can't shoot the weapon until you have someone in your crosshairs, which again is not how artillery works, it's how guided missiles work (at least in part).

How about making artillery weapons shoot without the need to have someone in the crosshair, but instead choose an area for the shells to land on? EIther as a quick pop up map where you choose the spot (likely dev heavy if at all possible) or by having a circle appear on the ground where your crosshair is which you move around to decide where to shoot, and...and you shoot:) a bit like this:

i

That's how thought they would work when I first tried them years ago (I expected I'd be able to use the minimap, e.g.). To do that and keep it fair though, they would have to ensure you can't drop artillery on arbitrary control points willy nilly, otherwise you'd be able to deny the oppos access to their home beacons right from the beginning.

Fair, then we could have some rules of engagement that perhaps you can only drop shells on beacons if they are being taken over, as is now roughly, or maybe having just had shells dropped on them the beacons would be a no-shell zone for say 15s, although that could backfire so probably the former is better as it virtually is how it works now. 

The way that artillery works now is you are shelling where the opponent was, vs where you think they are going. The way I propose let's you do both.

There most likely not enough of a cash draw to add more mortar type weapons. It's certainly not creating a  balanced weapon. with their track record balance is not their 1st priorty. It's design, make it powerful(overpowered), cash in till sales drop and than balance it to make room for the next overpowered weapon release. 

I got another idea, how about we don't think about this type of weapon just from the perspective of a mortar type weapon? since from what i read the weapon type is called "Artillery" and there are more than one type of artillery weapon, not just mortars.

So for a legendary artillery. how about we keep it basic? Perhaps a cannon that fires a high explosive decently good damage shell? and instead of having a reload mechanism, how about having it work the same way revoker does? increasing the firing rate the closer the target is? this way we have a weapon that can fire from long rang AND mid rang while staying effective.

edit: And to keep it fair, the closer the target is the less damage and splash radius it has. This way we don't end up with a weapon that destroyes everything from close rang.

Perhaps dispensing persistent landmines rather than bomblets might work.

I'm thinking traditional artillery. One round, large blast radius. Option for direct fire. A close range beehive round option would be nice, especially for use against those pesky, cloaked bots. This would also make the weapon useful even on indoor maps.

played a lot of missions with artillery on control points maps, it has it's own fun when you play with friends.. when i saw a lot of enemies in same place i would pick artillery mech when i died, worked out ok :) i think if one enemy is using it i have nothing against it at all, it's not that easy to do kills with it. But if many enemies used it, it would get annoying.. add legendary to that and it would get even more annoying.. so im still against legendary artilleries..