When you demand iOS users with a different opinion than you to "just buy the Android phone that supports the features you want"[1] and "just buy an Android phone with the features you want",[2] you are demanding others to make a personal change regardless of whether you want people to call you out for it. That is gatekeeping ("To limit another party's participation in a collective identity or activity, usually due to undue resentment or overprotectiveness")[3] because you are saying that people who support sideloading (an opinion that you disagree with) should not be iOS users. I have never told you to refrain from being an iOS or Android user for any reason, so I have not done likewise for you.

An iOS user who prefers to be able to sideload but also wants to, for example, stick with iPhone hardware is perfectly within their right to stay on iOS and take advantage of the benefits provided by changes to the regulatory environment. The momentum of legislation suggests that these iOS users will eventually get what they want without needing to switch ecosystems. Allowing iOS users to sideload by removing Apple's anti-competitive restrictions increases consumer choice, and benefits everyone except a minority of people in any country (Apple employees, those who have a significant ownership stake in Apple, and those who strongly identify with Apple's profitability as a company). Lawmakers are correct to prioritize the economic growth of their country and the consumer choice of the population at large over the interests of a small minority of individuals vested in Apple.

There are no significant negative externalities to allowing sideloading for iOS users, because only the people who want the feature will go out of their way to enable it, as user behavior on Android shows. There are significant positive externalities to enabling sideloading for iOS users, because removing Apple's anti-competitive restrictions would spur the development of free and open source apps that improve the experience for all iOS users who choose to use them, which increases the value of iOS as a platform and the value of iPhones and iPads as products. Developers have always had the right to "change the ecosystem" by pulling out from Apple's App Store whenever they wanted. It is their choice whether they want to have a business arrangement with Apple, not your choice or mine. Apple retains the right to impose restrictions on apps in their App Store, which they can continue to make the default app store on iOS. There has been no "collective bargaining" regarding Apple's App Store since Apple is a single company with monopoly/duopoly power, and we have not yet seen multiple developers (together) negotiate with Apple. Apple and Google do have duopolies in the mobile operating system market (iOS and Android) and the mobile app store market (App Store and Play Store), because their combined market shares make up most of both markets.

Many iOS users in China who want to use iOS apps that are not in Apple's App Store selection for China would definitely sideload these iOS apps once Apple's anti-competitive sideloading restrictions are removed from iOS.

[1] https://news.ycombinator.com/item?id=30220869

[2] https://news.ycombinator.com/item?id=30225190

[3] https://en.wiktionary.org/wiki/gatekeep