HK is wealthy because of where it is. Good luck trying to replicate that in the Falklands or on some rock in the Caribbeans.

Historically that might have been the case, today HK is rich because of its (financial) regulations that was mainly inherited from the british. HK is still one of the incorporation centers of the the world (akin to Delaware in US) as well as a major financial hub.

This is because it's the main route for money going in and out of China. Pretty much all of the commercial activity in Hong Kong is either trading/investing activities with China or facilitating trade/investment in China

Clearly, once HK loses the remnants of its autonomy and becomes literally a part of China rather than some external middle ground, it would no longer reap these benefits of its geography.

Geographical influences do exist, but the exceptions are quite significant.

Britain was once considered a backward periphery of Europe. Japan is so geographically peripheral that it could successfully close itself off the rest of the world for 250 years.

On the other hand, there is no Yemeni/Somali equivalent of Singapore even though a lot of the world traffic must pass around them. Gibraltar is rich, but Spanish Andalusia all around it has pretty stagnant economy oriented on tourism. Panama kinda works, but nowhere near as well as, say, California or Florida.

There are obviously legal and cultural variables allowing for the geography to be leveraged, as @iheartlife fairly pointed out.

But you still need something to leverage. Distance from population centers matters, trading routes matter, topography matters immensely as well.

Britain rose in conjunction with Trans-Atlantic trade. And so did Japan with Trans-Pacific trade and the development of the American West coast.

HK is an I/O hub for one of the largest economies in the world, it doesn't get much better.

An hypothetical Neo-HK somewhere would have to forcefully re-route the world's economy to have a chance at getting the same standing.

Previously significant, geographical constraints matter less in today’s globally connected world. Arguably, becoming more important in relative terms are mindset, creative and strategic thinking, willingness to work both smart and hard—and those would be in abundance.

Admittedly, Hong Kong benefitted a lot from being the convenient middle ground where major deals between entities in mainland China and other countries could happen. However, it can also be argued that meeting in person to shake hands might not remain a given going forward.

> the British could just give us some island they don’t need

What about the people who are already living on that island, what if they dont want foreigners?

It wouldn't be the first time a local population were forcibly evicted from a British colonial possession and a bunch of foreign nationals moved in: https://en.wikipedia.org/wiki/Diego_Garcia

There exist uninhabited islands, but climate is harsh.

This isn’t exactly a realistic proposal for many other reasons as well, but it’s interesting to contemplate.