Whenever people ask you why China is sees as a threat, you can simply quote the sentence you just said (Highlight in Bold) and even you will know why.
Problem is, while what you said is indeed correct, China is merely going after their own interest, but it's not the "Goal" that set the term apart, but the action, ala, how China get to the point of "Securing" their interest.
Let's use the US as an prime example. US have its interest in North and South America, and believe it or not, US and Mexico was still head to head, toe-to-toe to each other less than 100 years ago, problem is, with successive US President, instead of threats and hostile gesture, the relationship mended in less than 20 years (from a hostile environment) to alliance ship, from Mexico publicly support German Business in WW1 to Mexico joined the Allies side and fought in Europe against the German in WW2.
How about Canada? In the 1930s, the Canadian draw a plan to invade US and defend Canada, while the US draw the War Plan Red, and tariff war waging high and hot between Canada and US during the great depression. What solve the issue? A talk between Herbert Hoover and the British Ambassador Howard in 1927 defuse the tension. Not when US go blasting they could, might and would attack and destroy Canada.
Mexico is small, compare to the United States, and even as with China, United States can crush Mexico any day of the week, they did not do that, instead, FDR promote the "Good Neighbour Policy" were to play a major road to the peace of the region, you never even heard of how US bully Mexico these day, that's because of that, not threat and gesture coming out of the US President reminding we can crush you anytime.
Foreign policy 101, you push, they push back, it does not matter big or small. Make no mistake, it is not what US said push those country to the US, it's always what China did, both US and China says a lot of thing, but a gesture worth a thousand word and when all these country can see is how "Aggressive" and how China can "destroy" them in a blink like you said, what do you think they will do? Roll-Over? Nope, they will look for someone who can stand the bully. And that's the United States.