During training we had to switch motorcycles (we started on 250cc, then after a dozen hours moved to 600cc which is required by Polish law to pass the exam).

I have felt comfortable on 250cc but moving to 600cc felt like I had to learn everything again from the start.

On 250 (140kg?) I could throw my weight around and cause motorcycle to do stuff while the same no longer seems to work on 600 (210kg?).

Overall I feel better and safer on 600cc because at highway speeds it does exactly what I need it to do and place myself exactly where I want without feeling that it is overpowered and that slight mistake with the throttle is going to cause me to loose control of it.

I tried a dozen different motorcycles from 125cc to 1000cc before I made my final choice.

One disclaimer is that I am rather cautious driver/rider. As an example I never drive/ride fast in relation to other drivers. I may ride faster but only so much so I still am able to react if they make something stupid. I also spend a lot of effort learning to drive/ride safer.

When it comes to pratical matters I think that for safety it doesn't matter much how large your bike is, as long as you are properly trained. 125cc or 1000cc, your prospects in an accident are roughly the same.

Smaller bikes (125cc or less) may offer better handling if you are not well trained and you panic but on the other hand they might be less agile in traffic where it is important to constantly place you away from blind spots of other drivers, etc.

The only danger comes from speed and acceleration. But if you are an adult and can restrain yourself to safe speeds I don't think larger motorcycle is less safe.

What I mean is that it is not the size of the motorcycle but the driver that causes it to be unsafe. And unsafe drivers may prefer to choose larger motorcycles because it allows them to ride faster.