[AndyV7o]

No, using the wrong oil by accident or as an emergency wont kill your engine.
Over time problems could occur, it isnt guaranteed, and depends on use, oci's, engine condition and other factors.
The different specs have elements such as hths and saps which make a significant difference in how it works in and protects an engine, so some are outwardly similar, some are markedly different.
The hths isnt the be-all-and-end-all of oil, its one of many factors. Saps tend to be more important. People get wrapped-up in viscosity and misunderstand specs. The old grading system of xW xx is outdated but very hard to replace thus it remains, with the emphasis being on the spec required.
Its hard to portray things without speaking of the extreme to make it understandable. 👍