Is that not because the LAFD opted twice to retrofit larger water tanks on the birds?
They were delivered with conformal 350 gallon tanks (same as Bell 412s), but as I recall the LAFD then opted to get 420 gallon tanks. That’s almost 600lbs in added weight if utilized.
And most recently in December 2011, they received added funding to yet again change out the water tanks, now to a 470 gallon version. All said and done they crammed another 1,000lbs of payload on the aircraft above original plans.
For the record the AW139 has almost twice the power of the Bell 412s. The Pratt Whitey engines produce 1679hp versus the 900 on the Bell 412s.
They're bigger overall. About 1000 pounds heavier I think. That probably makes it feel a little more sluggish than the 412. But surprisingly, it does apparently carry more water. It doesn't look like it could, but it does. I haven't seen the latest tanks. I assume they must extend out the sides a bit or something.