I think there are two types of suburito in this thread. There is the common suburito (slightly heavier than a bokken, maybe resembling a tachi in size and diameter), then there is a heavy training sword. I have seen/used both but for different reasons.
My bokken has been treated with linseed oil for 10+ years and is heavier than normal bokken (more like the weight of those dynawood weapons Bujin sold). These are good for form and correctness and why I continue to use my bokken as opposed to the newer swords that resemble a chopstick.
The other training sword is almost too heavy and simple prohibits poor use over a prolonged period - these guys get upwards of 10 lbs. or more. We have several that range from 4" diameter branches from trees to 4"x4" posts, both with handles cut into the wood. I think these are great for building center and swinging a sword with your body.
As for injury, I think you are more suceptible to ligament or muscular injury (such as tendonitis) from incorrectly swing lighter weapons for a prolonged period of time than swinging exceptionally heavy weapons, which you can only do over a long period of time if you swing correctly. Although you probably have greater risk for muscular injury swinging a weapon too heavy for you body to use.
As for how suburi training affects cuts with a real sword... Matching the angle of the cut to the angle the blade assumes in your hand (hasugi) is tough and cannot [truly] be replicated using a bokken or suburito. I tend to think of the two cuts like to old TV knobs; one is for clicking between channel frequencies, one is for fine tuning the picture. If you have the right station, it is much easier to dial in the picture. While the two are not undifferent, there is a precision to cutting that bokken/suburito to does not provide. Much like splitting wood; swinging an axe and splitting wood are similar, but different. Swing an axe does not require precision, splitting wood does. If you have ever seen someone splitting wood and poorly position the cut stroke you know what I am talking about; there are many injuries related to poor axe cuts that deflect from the target and bounce into the leg.