Why hasn't legendary sniper cannon been nerfed?

I found the legendary sniper cannon didn't get nerf but common, uncommon, rare and epic are all nerfed.

Same problem happens to ballpark mortar, the previous update increase the damage of ballpark mortar but the legendary ballpark mortar didn't get the increased damage!

It has been months since that update but still no change to this two items. All the problem happens to their legendary rarity.

Please fix it or tell me why these two items are special from others!

Reedit:
I give some examples to explain this. Of all the rare items, level 50 rare item should have a little weaker stat than legendary level 1 item of same kind. However, the sniper cannon at legendary level 1 has much more damage than rare level 50 sniper cannon, which the legendary one didn't get 7%(I couldn't remember the specific stat) dmg reduction.

Same happens to Ballpark mortar, the legendary level 1 ballpark has less damage than the rare level 50 ballpark which didn't have the 14% damage increase as the update said.

All the data mentioned above are based on the shop which aren't influenced by perks.