I agree on the slowdown thing, it is normal in a way.
But only if you consider that Apple should only do hardware to make 45% profit on it.
And this is where I disagree, a lot more Android phones are sold every year because in the end people break/lose their phones, they become insufficient for their needs or they just don't have the means to buying a luxury phone that should be a useful tool first and foremost.

While people are largely irrational when it comes to Apple stuff (the "reasons" people buy iPhone are largely emotional for the vast majority or buyers) they are not entirely stupid and Android phones have become much cheaper for very comparable hardware, when they will have to renew, they may switch. It's definitely a problem for Apple even if you don't think so.

In my country a base iPhone 15 is 970 euros while you can get a Pixel 8 for 600 euros. The phones are very comparable in hardware quality, there is no way an iPhone is 60% better. And there is no way it's going to provide 60% better value over its lifetime, that irrational "thinking" (emotional behavior) that comes with the purchase of luxury products. And I think it shouldn't be a luxury product, it serves no one but Apple to have a tool become a luxury status symbol. It's worse than other luxury products because they don't get a market share as large and they don't influence the purchase of other goods/services as much.

Android is as insecure as you allow it to be. No one I know with an Android phone ever complain to me about Chinese malware. And I'm the tech guy and I get asked about bugs, installation of 3rd party stores, ad blockers, rooting, DNS bypass but no malware. And many have Chinese phones (Huawei and Xiaomi mostly).
You just have irrational fears instilled by bullshit marketing and emotional "arguments" from believers. It's a bit like the alarm salespeople who find a way to sell their "solution" that costs more overtime than what it is supposed to protect. Good sales pitch, I guess.

As for the hardware, Android phones do not become obsolete quicker than iPhones (quite the contrary in fact). Since Google and Samsung announced 7 years of support, that cannot be a valid argument anymore.
Also, I know from experience that Apple is, in fact, the one to blame. Under the guise of "free updates" they make their hardware become too slow or insufficient in a way that makes it borderline useless while not even providing all the functionalities announced in the update for older hardware.
How nice of them to save themselves the trouble of actually supporting an OS instead of conveniently just pushing a single OS on everyone to ease their maintenance burden even though very few will actually want/benefit from the new stuff.

For example, when I sold my Apple Watch Series 3 it became impossible to update it without erasing the whole thing. It received no worthwhile functionality in exchange, most of the new stuff was locked to the new watches (precisely the reason I changed in the first place) and the new software made it slower and have less battery life. To add insult to the injury, it is impossible to go back on an update so you are basically stuck with hardware that is not completely useless but has lost much of its value as a tool. All that to keep the thing compatible with their phone OS.

The only reason I didn't feel bad about selling it is because I sold it cheap to a friend and I take care of the issues for him and he just uses it as a simple watch. He wanted to look cool without spending too much money and he has no use of any of the functionalities, which is the majority of Apple Watch users in my experience.
I use it as a sport watch (swimming/running) but my next one will be a real sports watch. Outside of that use case it's pointless and Apple behavior around softwares/update is too bad to invest more money in a product that is lackluster and deeply flawed despite all the years/profits they had.

I think you are largely convinced by emotions about Apple stuff. They have some benefits and are well made but as far as my experience tells me, the major benefit is mostly how people will look at you.

It's a bit like arguing that a BMW is a better car than a Toyota. Yeah sure, but in practice both will let you lose your permit (depending on model, one much faster than the other) and both will carry you to the same places if they are functionally comparable models. But some people still get the BMW, not because there is a particularly good reason for it but because they like how people will look at them and treat them because of it. Unsurprisingly most of this group tends to be young males.
The iPhone is basically the same, expect it is a different target demographic, that is larger (younger person, predominantly females).