Economic size is the basis of power.
The bigger the economy, the greater the taxable base. The greater the taxable base, the more fiscal revenue the government can get from the public. The more revenue the government has, the higher the spending budget of the government.
The government can spend as much as it wants, but if they want to spend way beyond what the government has in revenue, then it has to run a big deficit.
If the government wants to increase spending and keep a small deficit, then it has to increase revenue.
The bigger the economy, the more revenue the government can ask from the public.
If the economy is small, the government don't have the ability to increase revenue as the economy can't support it. This causes the government to run massive deficits if it wants to increase spending.
China can dramatically increase the spending and keep a small budget deficit if it demands an increase in revenue from the taxable base.
You clearly have limited thinking skills, if you think the size of an economy is irrelevant
Japan does not have any hegemonic designs , nor is it flanked with a vast land border, so therefore it does not to prioritize a large standing army as compared to regional partners such as India, Indonesia, China, the Russian Federation, South Korea, North Korea. There are no designs on the JSDF to invade any nation unilaterally and neither would such an action be of benefit for Japan -- given its imperative to maintain its diplomatic relations with global partners and its dependency on trade. Don't translate our Government's security concerns regarding the Senkakus as some kind of inkling of Japanese designs to invade or conquer nation A, B, C or D. Because that is just absolutely not so.
Well in this case..... you're clearly under estimating the JDF... Actually i wonder if you can break their defences... And if your stating to the Senakaku Island its very tough for both parties to finish the task...and there's no way for China to put 2 million troops on that island ir it wouldn't need 2 million troops for that job..
To quote an old adage, 'Don't make a mountain out of a molehill'. I think this is a pertinent message for our regional partners -- especially in translating the context of Japan's defense expenditure and equipment purchases.