Anyone can call for changes in the regulatory environment to make a market more equitable for them. The difference is that you are demanding other people to make personal changes (going out of their way to buy a different phone, re-purchase all of their apps, and switch ecosystems) to satisfy your preferences and not theirs. Others aren't obligated to follow your demands, which is why it's not your place to demand them to act against their own wishes. On the other hand, nobody is demanding you to do anything. If the regulatory environment changes to prevent Apple from suppressing consumer choice on iOS, you can continue doing what you are doing now (purchasing and installing exclusively from Apple's App Store) as if it never happened.

Sideloading might not benefit you if you are committed to never using the feature, but it benefits other iOS users. There are iOS users who want to remain on iOS, while accessing apps that Apple has blocked from its App Store for various reasons. iOS users who want to use secure messengers like Signal, certain VPN apps, and other apps banned in China benefit from sideloading. Fortnite players who want the latest version of the app on iOS regardless of the ongoing legal case benefit from sideloading. There are also iOS users who are mostly content with Apple's App Store, but would gladly sideload other apps that are not available in the App Store, such as alternative clients for services like NewPipe, SMS/MMS apps with features that Apple doesn't provide, and FOSS apps that developers don't want to pay $99/year for the rest of their life to keep in the App Store. Sideloading provides benefits to all of these iOS users, without affecting people like you who wouldn't use the feature. You don't get to gatekeep who can be an iOS user, because nobody else is obligated to listen to you.

Most iOS users will continue to get apps from Apple's App Store even if sideloading were allowed. Google allows sideloading on Android with restrictions, and almost all users get apps from the Play Store in regions where it is available. There is little reason to believe that the situation would be different on iOS. If a developer does pull an app out of the App Store, that is their right to choose not to serve users in the App Store. You cannot compel others to make a business arrangement with Apple, because that is their decision to make. You are also not entitled to force any developer to make their apps available to you. Having said that, I have yet to see any high-profile Android app pull out from the Play Store without returning soon after (excepting those that discontinued Android support completely), and the situation on iOS and the App Store will likely be the same. Apple would still be able to impose the fees and restrictions that they want on apps published through their App Store.

I will continue to note that Apple's iOS restrictions are anti-competitive, because they prevent other app stores from competing with Apple's App Store on iOS. Walmart is not selling homes that require the homeowner to buy all of their groceries and appliances from Walmart. Also, Walmart and Kroger don't have a duopoly in any country, while Apple and Google do in many countries. Duopolies and other uncompetitive markets are not free markets, and they don't accurately reflect consumer preferences.