Because if we only limited to what can be used in canon, we would run into NLF's abound and end up with shit like "Sharingan cannot be defeated by anything but another Sharingan user" nonsense... or just see what happens with JJK wank. I don't really see how the first part doesn't also fit within fan theories because Goku never destroys a Star in canon, hell, it's fan theories that ultimately allows Goku to be atleast Solar System+ alongside his son at the end of the day in DBZ. Like I get your point, I actually do, we used to have someone who constantly expounds against the overusage of calcs to define a feat but here's the difference: He only did that because in most cases, you can easily just eyeball the feat and overrelying too hard on calcs has people see them as the only way to debate(Which we had when it came to the most basic shit in the recent Bleach Anime Arc). What you are doing is the exact opposite in that we shouldn't rely on calcs because you can use the canon...