If it's an AT&T Note 9.... WHY? Sim would probably work just fine in it, since you're likely just using AT&T or another compatible network.
I've heard this "Samsung is doomed!" line for years. Not quite as much as "Apple is doomed!" of course. I just don't see Samsung shaking that much, though it'd be great if they did. Competition is awesome, and it would push prices down, quality up.
Chinese makes still face a huge uphill battle though in the US market. Huawei being shut out of the US for possible spyware issues didn't help much.
Personally, I've looked at Chinese makes vs. Samsung, and just never found the quality that great. There's always been (for me anyway) some corner-cutting that didn't suit me.
I find I'll think.. sure... if I HAD TO I'd probably use this and be happy with it. But I don't HAVE TO. And I haven't seen the phone yet that'd take my Note 9 out of my hands.
I'd love to be wrong. Maybe if all the makes can get off the 'copy Apple!' bandwagon. I messed with a couple Chinese smartphones that PURPOSEFULLY used a notch that was 100% unneeded to the devices, but it's clear they are just grafting on such things because they think it's hip and "all the rage" and so it's us too! us too!" Still copying the iPhone X, a phone IMO, no one still gives a rat about.
The biggest problem I see (and again, hope to be wrong on this) is that these companies don't innovate- they copy and even steal- they ride the bandwagon. Its possible that if Huawei led the Android market the way Samsung does now, it'd just be "GREAT! Now we can give everyone iPhone-Lite like we want!" For those of us who like Android because it's (for the most part, let's exclude Google itself from this shall we?) NOT trying to be an Apple copycat- that'd be a disaster.
But by all means, give Samsung some real competition based on better features and pushing the true potential of the platform (nope, not you Google!) and I'm all for it. Would be a great thing for consumers.
I'm not keeping the note 9 because I still owe money on it, and the remainder is more than the cost of a used note 9. Rather just give it back and eat the fees, bill going from $335 to $60/month, it was worth it.
I think your info re: chinese brands is a bit dated. I would agree with you 5 years ago when I had my horrible Alcatel, but what chinese makers have mastered is rapid iterations, trial and error craftsmanship, and perfectly tying the software to hardware (like apple and google, i love pixel phones). Instead of making a silly comparison between a $1000 flagship and the lowest end xiaomi, i'll just focus on the positives of xiaomi's focus on polish and software perfection vs samsung's feature bloat:
1. Notifications on the xiaomi are instant. I have missed many a "pick up some milk!" facebook messenger messages because it felt as if my galaxy had to poll to get push messages, while my xiaomi dings the moment I get a message
2. bluetooth connects instantly: i used to criticize android's bluetooth stack because my car's sony system would rarely autoconnect without issues - often rebooting the galaxy note every day helped, but sometimes connecting would require a "turn off bluetooth, turn on.. forget device, repair.." dance. I just assumed it was normal. the xiaomi connects within seconds of turning on the car, like my wife's iphone. likewise, chromecasting to my sony tv is now twice as fast, though i can't think of a good reason - the a2 lite just makes that initial connection faster.
3. battery life. on paper, the note 9's battery life is great. USE the phone, and it's merely ok (day an change). my cheap xiaomi is going on 3 days now
4. Memory management is fantastic on the xiaomi - i would reboot my galaxy daily because slowdowns happen. too many tabs, etc. etc. app loads are a hair slower on the a2 than galaxy note, but reloads are consistantly instant. the note on a good day will load the app and do a split second refresh, the xiaomi just loads the app
of course, this $170 device has compromises - the build quality, the screen is not bright enough, the damn micro usb slot - but i'm getting %60 of the functionality at a fraction of the price. Customer service costs money too, you're paying for more things with a major brand, so I"m not being completely fair. But with xioami much of the benefits are software based in my opinion, samsung could catch up but xiaomi is there now: their $300 hardware can take on flagships. THIS generation has to have samsung worried - look up reviews for the Redmi Note 7, and look at the low light pictures, which wipes the floor of the s 10. For $189! Howd they do it? Commodity sony sensors and great software, probably reverse engineered from the pixel to be frank. and my post wasn't hypothetical - you;re wrong, samsung IS worried - the A series and M series were created to try to win back market share in china and india (and now europe), Xiaomi is in the lead with huawei in those crucial markets. when the galaxy represented the best (Best camera, but fluidity, best connectivity and features) it's asking price makes sense. I think pixel (other than the god awful design) has taken that lead leaving samsung among the rest of the good enough.