The tech industry is pretty big
When I think of great companies in that space, none of them are glorified walled garden digital storefront beneficiaries that merely take a transactional cut. At least Apple also makes great physical products with great software
Steam could go away tomorrow and the industry would be just fine on some other platform
Apple makes a great physical product at about the same cadence that Valve makes a new game, not that often anymore. Beyond going ARM with their M chips being a smart choice, everything else about them has been iterative boring hardware since Steve Jobs died. Their VR headset barely innovates anything, their hardware breaks more than people would admit, and they're still anti-consumer to moon on top of most of their product line being overpriced. Valve has done more to make the platform better through software services (Steam Input, Proton, Big Picture Mode, etc.) that actually add value other competing companies don't, while I can't think of a single piece of new software in the last decade Apple made that wasn't done better by a third-party.
Valve isn't without criticism, but pretty much all tech companies that aren't the major hardware makers for fundamental components like semidconductors could die, and the market would adapt fine because there is competition in every major space.