I’m not sure what the point is of arguing on the historical legal status of Taiwan - it might be an interesting academic exercise but it won’t matter a smidgen on how the PRC, USA or Taiwanese governments use their interrelationships.
In fact that is one problem of Bellochi’s criticism of Gilley’s article. Gilley does not use his assertion that China and Taiwan split in 1949 as a premise to his argument. It doesn’t matter a jot if it happened in 1949, 1895 or 9843 BC.
One of Gilley’s arguments is that Taiwan should take a neutral stance rather than strong alignment with the USA. It should become a non-militarised state next to a powerful country - the same way that Finland remained non-militarised next to the Soviet Union. In return China would give Taiwan further status internationally. China can use its economic power block Taiwan’s participation in ASEAN or for that matter with most countries in the world. By being left out of ASEAN Taiwan is at a serious competitive disadvantage, particularly from South Korea and Japan.
Taiwan would also be allowed to keep its self-determination as long as it doesn’t do anything to threaten the PRC’s strategic position.
Gilley’s premise is that the PRC does not want to take over political control of Taiwan but is seeking strategic military control of the region. Gilley asserts that China wants “…a sphere of influence that increases its global clout and in which Taiwan is a neutral state, not a client state”.
As evidence of this he cites examples of how China’s diplomatic language has shifted over time and in response to Taiwan’s actions, and how surveys show that popular opinion in China is against military action.
Unfortunately Bellocchi’s article does not really provide arguments against this one central premise - apart from citing issues in Tibet and “East Turkmenisatan”, as if China is still under Mao’s expansionist regime of the 1950s. Bellochi simply states assertions about not giving in independence, and shouts appeasement as if Taiwan is the Sudetenland in Czechoslovakia - where Germany took over both military and political control.
Gilley basically says that Taiwan needs to trade its card of being a militaristic strategic lynch pin in the area for continued economic prosperity. It’s not about ceding political control.
Gilley also says that by developing a more neutral military stance to Taiwan, it has a better chance of changing China’s politic than if it stays essentially confrontational - in the same way that Finland’s neutral stance was a lynch pin that led to the collapse of the Soviet empire. This is actually a weak argument as there is little evidence as to whether being neutral or confrontational will have any effect on the China government.
Nevertheless, Gilley provides a choice - trade in your strategic role, or remain an economic outcast.