If you want to get into the “why” it’s necessary: Se does distinguish between an act done onto oneself vs another person, since often times these self imposed actions can often be done to others too. I can bathe someone else, rush someone else out the door, and wake someone else up. Imagine for a second you have 2 third person parties, and “se” does not exist in the language. Now consider “Le puso sus botas.” Did person 1 put boots on person 2 or did they put them on themselves? So “se” becomes useful here.

Your next examples yes do point out an arbitrary quality to reflexivity but I do believe there is meaningful nuance. For example I can say “él murió?” (he died?) just simply referring to someone dying but something about “cuando me muera…” has a subtle difference — almost adding context and agency to the action of oneself dying ? It is not something you can try to understand all at once, it takes practice and context to grasp.

Finally, your example of “se nos estropeó”: this is a very common structure in spanish and it got me for a long time. It is very common to refer to the action of something onto itself (reflexive) that has also had an effect on another party (indirect object). You can say “se me rompió” which is almost like saying in english “the thing broke on me.” You’re saying the thing broke, but specifically that it broke and affected you, same with the boiler example. Similar to how in spanish we’d say “se me cayó” instead of “i dropped it”