Whether litre class, 600 cc or not. There is no term such as Heavy Bike in the world. It's just a result of jahalat.
I know this because I learnt this the hard way. A decade or so ago when I was in college, I used to call them heavy bikes too. And then I went abroad for studies. I clearly remember that day even now, when I entered a bike retailer in West London, just for window shopping even though I was posing as a prospective buyer.
I kept saying Heavy Bike, Heavy Bike to the sales man, and he was just staring at me for a good 5 minutes before saying, "Heavy Bike? What are you looking for exactly?" And I kept repeating Heavy Bike, Heavy Bike. After a good 15 minutes, he said, "I don't know what a Heavy Bike is. Can you pinpoint from the bikes that are on display here."
I quickly pointed my finger towards a white R6 there, and he went, "Ah, those are called Supersport or simply Sport bikes." I was so embarrassed at the time, that I had to apologize and thank him for correcting me. I have not used that stupid term, Heavy Bikes, to-date.
A bike being heavy has nothing to do with how fast it can go. Actually it's the complete opposite. All bike manufacturers fight to keep the weight of Supersport bikes as low as possible to make them more competitive every year. So, there is no direct co-relation between them being Heavy and being Fast.
And it's NOT just the 1000cc bikes that are called Supersport, but all including the 600cc or any of the sport configuration bikes with a small engine capacity. Even the 125cc, 300cc etc. bikes come under the Supersport category.
To confirm this check the link below. You will find KTM RC 125, RC 390 and the mighty 1190 RC8 R under the same SUPERSPORT category.
So, the bottom line is that the word, Heavy Bike, is a result of ignorance and jahalat more than anything else.