I haven’t ridden the 650R, but I did a new (800cc) BMW F650GS. It makes about 5 foot pounds more torque. That puts both bikes at just over TRIPLE the torque of the Ninja 250. Let me be clear on this, if I’m heavy on the throttle and quick on the clutch I can get that front wheel light without trying. I’m certain with practice I could wheelie the 250. I’m even more certain that I could wheelie it by mistake if I really buggered things.
Wheelieing a bike is not smooth and elegant like they make it look on TV. Unless you have good balance and the bike goes up perfectly stright, it is going to come down on its side, or turned enough that when it hits down it’ll steer violently to one side. And unless you expecting it, it can be a pretty scary thing even when everything goes right. Youtube is full of the failures. I recommend you watch them.
Now, again, I can’t speak to the 650R or other riders. But if I made the same mistakes on the F6560GS that I’ve made a dozen times on my 250, well, I probably wouldn’t still be in this sport.