Re: Reasonable weight for suburito?
Thought of something else (sorry if it is too much info, but I'm a geek that way).
One thing to check is your usage of your shoulders. If your shoulders are "separated" from your torso things tend to get that "fluttering bird" look when you cut. One thing you can try is to get the sword up into the high guard position. Now make sure your shoulders aren't lifted up. Try to keep them settled into place, connected, not rotated up towards your ears like you're shrugging. Do a cut slowly keeping the shoulders more "controlled" during the cut. Don't let them get out too much, but of course there is some movement. So chudo -- middle path.
You can also add to this a feeling when in high guard that both gravity is pulling your arms down (weight underside if you will) to make sure you don't flare your elbows too much. Then also feel like you're already cutting forward although you're not. This is sort of difficult to describe but I'll sometimes get a student into high guard then stand to the side holding the tsuka myself and putting a little pressure backwards telling them to hold the blade still. So I"m trying to engage a forward feeling. Then I remove my hand and let them cut. The idea is for there not to be a separation. No chambering. Just cut by letting your arms rotate as you reach forward keeping the shoulders in.
Now having said all that I wouldn't be remotely surprised to have someone post "all that is absolutely wrong in our style". So... $.02. Grain of salt. Etc.