Dear Bioblaster

[Blueyes]

This wasn't a balancing decision.

They literally just lifted the skill from old PVP without changing anything.

I'm willing to bet they didn't even notice that they'd grouped a 12y skill into a rotation with 25y skills.

They simply didn't think about the implications.

Pretty much this. It actually may be more accurate to consider it a purely aesthetic choice. Drill, Bioblaster, Air Anchor, and Chain Saw all utilize MCH's big "multitool" whereas their other actions don't. That's the only reason why those four actions were paired together. I don't think consideration was taken for how the inclusion of Bioblaster would negatively impact the flow of the job.