Maybe. maybe not.
I started on a 750. A zephyr 750, which is one of them UJM. Definetly not a sportbike.
And at first I too thought that a 600 would be a fine starter. Hell, I thought that even a liter goes only as fast as you want it to.
Then I meet some kid in a parking lot talking about his new bike. half an hour later I'm pulling him out of a ditch. a month later, same thing. I find myself spending all saturday in the ER, waiting to hear on some kid I've never even met before. He had no family around, I figured someone has to be there for him. The same story repeats itself time and time again.. And let me tell you it gets old real quick. Nothing like the sight of blood and dismembered body parts to ruin your weekend.
So I went back to my thinking. I stopped with the attitude I have of "I can handle just about any bike, without getting in trouble" and thought about how I was riding when I first started. How I had to slow down to 3 mph to make a street corner. How I amazed I was when I figured the concept of counter steering, and "reverse countersteering". How I dropped my bike in the middle of the street becouse it stalled on me.
I really dont think its the horsepower thats a problem. Even a 250 can easily reach speed which will seriously hurt/kill a rider. Hey it doesnt take much. 30mph can be fatal.
But the responsivness of modern sportbikes is hard to deal with.
Less sporty bikes will stand up under braking. Thats really annoying if you are trying to haul ass, and brake deep into a corner. But on the other hand, available traction increases as the bike stands up, thus locking up the front tire is a tad harder. It takes time before you can feel the front brake, or the suspension. With some expirience, the bike talks to you, tells you whats going on. But not when you are new. Not when you got a death grip on the bars, every muscle tense, adrenaline surging as you pull out of the parking lot.
sure 600's are fun. I love stabbing away at the shifter, dropping 4 gears before a corner, trying to blip the throttle just right, so that I can hear the engine scream at 13000 rpm, rear tire sliding leaving marks on the pavement, as I set up to brake for the next. But the idea of either tire, sliding even a tad, was absolutely terrifying when I started. Hell leaning past 45 deg seemed insane. The bike could just fall at any moment.
Being a heavier guy only makes the problem worse. Sure the bike doesnt accelerate as hard. But the center of gravity is higher, which means the bike is twitchier. It means that any change in riders position going to affect the bike more. Does a new rider realize that? probly not. He will most likely continue to shift his weight, sending his bike into a bizzare wave instead of a line.
Can a 600 be civil? sure. But what happens when you get a little brave? Just a tad, just enough to push a corner at 10 mph over that "recommended" speed. And a deer jumps out in front of you? or there is an oil slick? or gravel? What happens when a sudden, panicked grab at the brake locks the front wheel, just for half a second, but enough to send the bars into a wild, ravanous dance. Enough to rip them out of your hands as the jerk from side to side faster than your eyes can see?
Or maybe you stabbed the rear brake, becouse you are afraid to touch the front. You feel the rear wheel slide, and it will slide so easily while leaned, giving way, untill you realize that very soon you will fall unless something happens? So you let go of the brake only to find the bike jerk so hard it throws you off, like a rag doll, and no matter how strong you think you are, you got no say in it what so ever?
So what do you do when you are flyind head first into the pavement, and your motorcycle now behind you, just far enough, threatening to run you over right as you make contact?