Isn't it better to use "brittle" instruments?
So we do not learn to gain too much "power" from our trainig weapons? [/b]
no. Simply because they are dangerous. Even in the hands of 2 real real experienced people they'd be a danger if they broke but in practice you're not going to have them in the hands of only real experienced people. A chunk of someone's weapon shatters, flys across the room and hits you in the eye or other location, you'll find yourself wishing they were made out of titanium.
Be glad you're not being told to use ratan sticks wrapped with duct tape and padded with foam rubber for safety instead of what you are being told to use.