This. Let's face it, this forum has more US members than from anywhere else and in the US, WhatsApp is next to irrelevant. It's just not used by most people. US carriers long ago offered, if not unlimited, huge quantities of SMS in our mobile plans so there was no need to use 3rd party solutions. Using Apple Messages required zero change in use behavior but offered tons of functionality and benefit over standard SMS/MMS.
Once you've become accustomed to those added benefits, it's harder to step back to regular SMS.
The Android Messages app has certainly improved from my past experiences--being able to message from my Pixelbook is nice and a limited approximation of doing the same with Apple Messages on Apple hardware. I also find the smart reply suggestions to be surprisingly (and eerily ) good. But the overall experience isn't nearly the same as if you use Apple Messages and especially across multiple devices. I'm managing fine but do miss a few aspects.
Android has a bigger market share than iPhone in the USA. Messaging is the major form of communication nowadays. You can't tell me 3rd party messaging apps in the USA are irrelevant when it's most likely the majority of the market (which is Android based) use them.
Whatsapp, Telegram, and etc are widely used in the USA. Don't know why people say otherwise.
And that's when your wrong. It's not the most restricted, it's actually the least restricted. iPhone users don't have to do anything to use it and be able to reach nearly ANYONE. If you have a phone number, it works. If you don't have a phone number but have an Apple device (ie. my kids for years only had iPods or iPad, same as their friends), it works. The only people you cannot reach are folks without a phone number and no Apple device...a pretty small % of mobile device users, expecially here in the US.
Any of the 3rd party apps you mentioned required an additional account and app. I can reach every single person in my contact list using Apple Messages. Can't say that about any of the other apps you've listed.
And that's where users are fooled. If the receiving or sending party doesn't use an iPhone, then you're just receiving or sending a plain SMS/MMS carrier text under the iMessage UI.
And yes, it is restrictive. You must stay on Apple's platform to take advantage of it. With the other major messaging apps, you don't have to worry about what platform you and others are using to take full advantage.