Not really separate. Many extensions designed for other browsers will still depend on quirks of the respective extension implementations, JavaScript engines, rendering engines, etc.
Of course, there are (supposed-to-be-but-aren't) browser-agnostic WebExtensions — but again, only Safari implements them on iOS (starting with iOS 15), they must be bundled with an iOS app, and non-Safari browsers don't have access to those bundled extensions.
Perhaps those browsers will implement support for WebExtensions by some other mechanism but it certainly won't be the case that Firefox for iOS could run extensions intended for Firefox on desktop, nor would one expect extensions from the Chrome Web Store to work properly on Chrome for iOS.
Perhaps that's an upshot? Better support for browser-agnostic WebExtensions?
Even then, that's up to whether or not Apple permits that in the App Store.
Of course, there are (supposed-to-be-but-aren't) browser-agnostic WebExtensions — but again, only Safari implements them on iOS (starting with iOS 15), they must be bundled with an iOS app, and non-Safari browsers don't have access to those bundled extensions.
Perhaps those browsers will implement support for WebExtensions by some other mechanism but it certainly won't be the case that Firefox for iOS could run extensions intended for Firefox on desktop, nor would one expect extensions from the Chrome Web Store to work properly on Chrome for iOS.
Perhaps that's an upshot? Better support for browser-agnostic WebExtensions?
Even then, that's up to whether or not Apple permits that in the App Store.