Main reason is because there are no Blast type bombs with Elemental damage. We have Nitronome/BAB for Normal, DBB for Piercing....But no blast bomb for Elemental.
Extra reasons :
> Deconstructor line is very unpopular.
> Deconstructor looks like gremlin bomb (and gremlins deal Normal + Elemental damage).
> Deconstructor line stops at 4* and that is no good.
So i suggest to shift Deconstructor line up one star, turning Deconstructor into 4* Elemental Blast bomb with dmg bonus VS construct Low
and Heavy Deconstruclor into 5* Elemental Blast bomb with dmg bonust VS construct Low.
These should have same damage as Master Blast Bomb / Nitronome respectively.
Alternatively, both Deconstructors can have split damage (Normal+ Elemental) with Medium damage bonus VS construct.
This Line will start after Super Blast Bomb.
Everyone has been saying something like this forever.
There's little reason to disagree. I mean, we could talk details. For instance, I'd be fine with 5* Heavy Decon having a lower base damage than Nitro with a High vs Constructs that puts it above effective DBB again.
Or you could keep all of Nitro's damage, keep the dmg High, and also keep the smaller radius; That'd make it quirky and interesting.
On the point that Decon should be 5* and elemental, however, nobody has any objections.