"Sounds like a jolly day out" = the point?
A 2012 GSX-R1000 weighs exactly one tank of fuel more than the 600, I'm not sure that weight is particularly significant unless you're playing Top Trumps. The consensus seems to be that ragged balls out, the road or track or rider is the limiting factor, not the bikes. The difference is torque and in-gear acceleration, which is what matters when you're not out trying to lose your license.
For once, I agree with MCN's analysis. 600s aren't cheap to buy or insure or run any more. If you've got the money and the desire to get one, you can probably stretch to a 750 or litre bike instead - especially since they cost essentially the same to make, so there will be more negotiating room in the litre bike's price. And if you can, why wouldn't you? Is there anything inherently more desirable about the 600, except that tank-of-fuel weight saving? Heck, it might even cost you more to insure than the litre bike - do some quotes, you might be surprised.
All that said, the best selling new 126-650cc bike in July was the YZF R6. Granted, there were only 82 of them shifted, but that still speaks to their being some demand.
Suzuki, by the way, sank to #10 in the sales figures, behind titans like Lexmoto and Direct Bikes. 319 bikes, fewer than 4 per dealer. That's not even a bike a week, and that's with all their cashback offers, extended warranty, AA cover, Uncle Tom Cobley and all. It's not just supersports 600s that are in trouble, Suzuki UK can't give their bikes away. I wonder when MCN will pick up on that?