Fine so continue in the walled garden, no-one will force you to use a 3rd party store. Easy.
The comment you were responding to needs more nuance.
Prior to this, it was easy to stay within the walled garden when it was the only place where one could get apps. As such, all developers had to go through the App Store. Setting aside the 30% cut (which is largely a dev issue), there are a number of benefits for the end user. iTunes means that devs never get to see your payment details, and it's easy to manage your subscriptions in one place. There's also ease of payment using biometrics.
You are technically correct in that nobody is forcing me to use a third party App Store or side load an app if I don't want to, but in the chance (however infinitesimally small) that there is an app that is available only via that App Store, then I either have to do without said app, or cave in whereas in the earlier scenario, that app would likely have been made available in the iOS App Store because there's nowhere else to go.
Even if there is a 99.9% chance that devs will continue to support the iOS App Store because that's where the users are, it's still a 0.1% risk I am taking that I never had to contend with before. There is zero benefit to me.
I am fine with the walled garden model because it has all the apps I need, while you welcome sideloading because there are apps you presumably would like to access that aren't available in the App Store. Regardless of the outcome next year, if one of us is to win, then the other will have to lose.
It essentially boils down to each of us wanting to have our cake and eat it too, and I don't think there's any shame in admitting it. We are all selfish like that.