All I can say is the Rebel hasn't been a 'step down' for me. It's not as fast as most of the bikes I've had but what it lacks in out right speed, it makes up for in other areas. It's so easy to ride, being small, and fast enough to be fun... and even fast enough to loose a license with.
I traded a 660cc MT03 in for the Rebel and still had a Bandit 1200. Subsequently, the Bandit has been sold and the Rebel remains! That should indicate something.
I don't understand this idea that a 500cc bike is for 'beginners'. Way back when Adam was a lad, a 500 was considered a middleweight that most people had/wanted. Litre capacity bikes where just for dreams and 1200cc plus bikes didn't exist.
At the end of the day it'll be your money and only you can make the choice. One thing I've learned over the years is that there are always other bikes tempting me to part with cash. Nevertheless, the Rebel has something that's quite endearing, precisely what I don't know.
Anyway, my guess is that if you're in any doubt, you should perhaps look elsewhere. I suppose your choice should depend upon why you want the bike and what you'll be using it for.
Good luck with whatever you choose... all bikes, whatever their size, are fun!