Valuation is not the whole story...
... or even a large part of it. Hell, adjusted for inflation, Apple's market cap is less than three times that of Yahoo's at the latter's 2000 peak - and Apple actually sells something. Market cap and other financials are important data, but to equate market cap with "size" is just foolishness.
In any case, Apple most certainly is not "the colossus that bestrides the tech world". Apple isn't even vaguely involved with most of "the tech world". They make consumer devices - that's it. They have essentially no presence in business transaction processing, for example, except to provide one of many channels for end-consumer purchasing. They have no presence in high-performance scientific computing. They have nothing in embedded computing, aside from their own consumer devices.
Embedded computing represents the vast majority of CPUs in use. High-performance scientific computing covers most of the cycles. Business computing is what has the most influence on the economy, and through it on the orderly functioning of civilization.
Apple has a relatively small share of markets like education and business productivity.
The only places Apple has a large presence are entertainment and high-end personal communication.
If every single Apple device in the world failed tomorrow morning, the effects would be pretty minor. You'd have a lot of panicking iWhatever owners. You'd have some bad effects on Apple stock, eventually. A number of people would suffer some distress because their phones wouldn't work; that might even conceivably cause some deaths.
If, say, every IBM mainframe IMS region stopped working at once, the global financial network would crash. *That* is a "tech colossus".