TBH, yes, it's a plus IF things were equivalent... If the BK9 were a G70 at 21 lbs, I would be the happiest guy alive. Sadly, it ain't. The action is still, compared to the G70, a lightweight (albeit, not nearly as light weight as the PSR series). I have taken the action out of a couple of G70's to work on (most of my friends with them get me to do minor fixes) and the action alone would probably account for well over half the BK9's total weight!
This translates into something that feels wonderful to play, yes, not as heavy as a full 88 wood, but that delicious compromise between flyweight synth actions and full weight piano. If you are playing both kinds of parts, this is the best compromise ever made, IMO.
Mind you, the same action was in the G1000/800, and they managed to come in a good 5 lbs lighter than the G70 (don't get me started about the MUCH heavier E80, which only had a synth action 61, but had a beefy speaker system!) so Roland definitely didn't have weight on their mind when they designed it! But the G70 is built like a tank, I guarantee it will outlast any BK9 that isn't babied carefully by its owner.
So, all in all, win some, lose some!
As I've said, simply because of the Chord Sequencer and the Audio Key feature, I'm probably getting a BK9 for solo work, and sure, I won't mind the weight while I'm carrying it! But the minute I start to PLAY, I'm going to miss that extra 24 lbs! But, truth be known, there's really only two times a night when I actually CARRY my G70... As I pull it out the flight case and put it on the stand, and when I put it back. The rest of the time, it is dollied. And, as I get older (and maybe wiser!) I have started to make sure my case is resting on something, raised up, so I don't bend to the ground to lift the beast out. So far, no hernias..!
And Donny... at less weight than most 61's, why would you even WANT a 61 version? Don't forget, that Audio Key feature chews up 7 of the top notes. That don't leave you much on a 61. And more notes with less weight, finally you can play proper piano parts (or real close, anyway!) without busting your back!
I'll be using the BK9 for solo gigs, but I'll still be using my G70 for all full band stuff (which is still the majority of my work these days), because what you play ON is still important...
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An arranger is just a tool. What matters is what you build with it..!