Shaft alignment: I've often wondered why the strut-cutlass bearing
isn't set up with a gimbaled cutlass bearing support. That would allow
easier alignment on the transmission end. Also, sail drives have a fairly
large diameter in the water to accommodate a gear case. The gimbal
would not have to be any larger. Cost maybe?
The aft shaft bearing needs to be rigid as it is trying to prevent a prop and shaft moving around. As you have thrust loads on a shaft from the prop there is a tendency for the shaft to flex and then whip or spiral as torque is applied. So that bearing is essential in keeping the shaft running true.
Rubber bearings ( I believe) don't help the situation but it will be a long time before people start to see the benefit of a hard bearing in the strut. Military boats use hard bearings to keep noise and wear down as well as a large number of commercial vessels.
But I'm biased I work with bearings and solve bearing problems for a living!