You can always build your own phone and setup your own app store. Samsung does.
I generally agree with your point, but this is a weird argument: towns can and do ban big-box stores, and yes, "move to a different town" is exactly the only remedy people have, if they want to live close to those kinds of stores. And frankly we generally see that as a good thing! Big-box stores tend to kill downtowns.
> I've invested considerably money into the apple ecosystem.
This confuses your Walmart analogy quite a bit, because there's no such thing as "investing money into the Walmart ecosystem". Walmart doesn't have an ecosystem. If your Walmart closes down and other stores pop up to replace it, you just start shopping at those other stores, and likely don't really notice much of a difference.
And that's precisely the point of the issue with Apple. If I've been an iOS user for years and years, and suddenly Apple changes the terms to something I really don't like, it'll cost me a lot to switch to another platform.
In the Walmart case, you've bought your house. Presumably up until now you've mostly relied on Walmart to furnish it, and to buy groceries, etc., etc. Walmart disappears. Your existing furnishings are fine and still work. You can buy more furnishings at other stores, and they will work just fine in your existing house, with your existing furnishings. You can buy groceries at another store, and consume that food just fine in your existing house. Also consider that Walmart has online ordering and ships things; if you really want to continue to get some items from Walmart, you can still do so.
Sure, if you're unwilling to take the entirely reasonable step of finding alternatives to Walmart, I guess you'd have to sell your house and move to a town that still has a Walmart. But that's... a pretty ridiculous course of action to take, honestly.
If anything, they’re hurting developers, but even that may be hard to argue. Developers still flock to the platform.
Even if those developers can’t make a living doing that (and many likely can’t), that’s not an argument for Apple’s fee being too high. There’s no right to be able to make a living in the way you want.