It's not my case. It's summary of ROC/PRC argument, which predates others and had garnered major international support in a time when these disputes had no geopolitical relevance. Now it does, so the the ambiguities in language gets re-prosecuted, and is exactly what everyone nitpicks over. China thinks it sufficiently transfers islands over to Chinese sovereignty, Philippines doesn't, hence the dispute. There's also historic claims vs UNCLOS regulation, what supersedes what with 6 parties + US, it's a mess. Really, the only viable settlement mechanism will be hard power.
Which is inevitable, even in the 60s when significant countries were fine with Chinese claims, these legalities barely mattered to resolving the disputes since no interested party had the power to enforce anything. There's so much resources and security tied to maritime control in this region that this is only a dispute that can be solved through force. Along the same lines, it doesn't matter what regional or major world players think about Chinese legal arguments if China can enforce it via tonnage. Right now the only viable opposition is USN + FONAPS. But that's kind of status quo US+China is comfortable with, everyone dick waves without touching tips.
The important point in terms of "claims" is where previously plurality parties endorsed Chinese legal nitpicks (hence China has the earliest and strongest claims), now they do not, not because other claimants have better arguments, but because geopolitical interests changed. The quality of the arguments do not matter, nor the laws if we're honest. China explicitly did not submit to UNCLOS arbitration mechanism, so the PCA ruling hack was not to decide on sovereignty but maritime boundary but defining what is / is not features to deprive China (and other countries) of EEZ and territoriality. Right now China "adheres" by limiting weaponization, and drafting other legal arguments to legitimize holdings for more territorial perks. But that's just a stalling tactic until Chinese Navy is large enough to control the region defacto.