I understand your point, and it has some merit. However, I have two points around that:
1) The model of multiple store fronts already exists for macOS, and what you're describing isn't an issue.
I made several points about convenience and security. Your response seems to be "There are other platforms that are less secure and convenient and I like them, so you should just live with my choice."
Security is an issue on macOS and is even more of an issue on the dominant platform (Windows) that is why anti-virus software exists for macOS/Windows and is not required for iOS/iPadOS/tvOS/WatchOS.
Many of the name brand companies don't bother going through the Apple store, but you know full well you can still trust the software.
I have no choice on macOS, but it is a much worse experience for me than that of iOS/iPadOS/tvOS/WatchOS. I have to find the store, figure out the rules for the software (Do they have some family sharing model? On how many machines can I run the software? How do I reinstall it? Does it have to be connected to the net to work?), create a new account and share my credit card information (which I have have to go find),
etc.
For the smaller ones, if I come across some software I'm interested in, and I don't know the company, it's really easy to do a quick google around for it and see if it's commonly used and if there are issues. It's very obvious if it's dodgy.
Do you argue against food safety inspections because you can tell from the packaging if it is safe? I understand that you are happy to spend your time researching these companies and products and do not mind creating a million new accounts with which you have to share your personal data. That does not respond at all to my point.
Millions of users agree with me and like the current model.
Regardless, more and more software is now being put through the Apple store on macOS, as I think many companies understand your point.
I do not want it left to their discretion. If you are ok with that, you have options (Android as an example).
In conclusion, I think you'll find that in reality it won't be a problem.
It is guaranteed to be a problem, because I never want to have to do it and we already know from the macOS that many of the larger players will make it so. I get that it does not bother you, but that does not change my view.
There will be a huge amount of apps that will stick to the Apple store as they know it will be the first place people will look, and they know it's trustworthy, so of the little guys creating apps, you'll have so much choice through the Apple store that you won't need to bother with anything else. Many of the bigger names might simply set up their own, or conglomerate to a couple of alternative stores with better terms, and you can decide if you want to trust, say Blackmagic or Adobe if they move to their own store, and I'm guessing you will be fine with it.
You are not even consistent in your statements. Most things will be in Apple's store, lots of big names will create their own stores, some new people will create other stores, but it will not be a problem.
That is exactly what I said I do not want and your response is "I understand, but I do not care because I want it."
Let me just go back to your statement and my previous response:
You will still have the choice to stick with Apple's walled garden if you want, and others will have the choice to not to if they want.
To which I said:
Once there are multiple stores, some products will only be in other stores. Now, if they want to serve me, they have to be in the only store. With your solution they will have a choice and that will mean I do not have a choice.
To which you responded: You will have to go to lots of different stores, but you should not care about that.
2) Apple rejects a lot of apps for various highly socially conservative reasons. E.g nudity, swearing, gambling etc (but high levels of violence are allowed, go figure). So at the moment, those of us that consider ourselves to be adult enough to make up our own minds about such things, well we simply can't have those apps (but we can of course get all that stuff via the web on our iPhones/iPads). In many ways apps are superior to a web app, so it is a rather lame restriction.
Again, you do not seem to understand that your option eliminates my choice of a platform without those things. Again, I understand that you want them. This is not the platform for you.
In conclusion, alternate stores will not destroy the vast number of highly trusted apps on the Apple store, but will merely open up choice, both for the developers that don't like Apple's rules, and for users that want apps that aren't restricted to Apple's twisted idea of family values. For proof of this, one only has to look at macOS for comparison.
Again, your response to my statement that I want a single store for many reasons and your option takes away that choice from me is to say in one breath that it will not have any impact, but it will make there be many stores that will guarantee fragmentation, but I should be fine with that. What you fail to acknowledge is that right now, companies and developers who wish to develop for this platform have to follow the rules on things like tracking and supporting Sign in with Apple. In your world those who have no choice and live with it now, will just move to a store where they do not have those restrictions and I will lose the option of a privacy preserving version of their app.
I am completely willing to give up porn apps for that level of trust.
Developers that do not like Apple's rules have a choice. They can develop for Android. If enough of them stop developing for Apple's platform Apple will have to charge.
Users who do not like Apple's choices can pick one of the many other competing options. Stop trying to ruin my platform by forcing me to accept your choices.