Yes, you are right. Welding the spider gears if done properly won't break anything.

Now if the diff is marginal for the torque output of your engine, then a spooled or welded diff can push it over the edge. Just like slicks will. With the H145 & H150 you are more likely to break and axle when the diff is welded -- if you have a high-torque engine.

Certainly for Antarctica you need a locked differential.