I've had oppo, Oneplus and Realme phones in the past.
All the same umbrella company. All uses the same parts as you'll find on your Samsung's. I've had European warranty and had repairs with them as well. Software updates are now much better as well.
If the price is right for you then I would choose them over the Samsung etc any time
Hardware is not really the issue, it is more the software. Many of these Chinese brands offer amazing hardware, but the software is quirky or buggy in many ways. RAM management is an issue in many models, with 8 GB phones kicking apps out of the active state despite only 3-4 open apps. Notifications not coming through, need to enable permissions from some obscure setting page, text messages getting delayed etc are some common issues i have found on phones by these brands, particularly Xiaomi and Huawei phones.
Oneplus has the best software implementation out of all chinese brands and it works well. It doesn't have all the gimmicky stuff, but it is efficient, fast and lean on resources.
I always prefer the likes of Samsung, LG, Sony and Nokia when it comes to the UI and software. The software almost always 'just works', with minimal bugs and odd behaviour of some apps.
If phones with great hardware and mediocre software work for you, great. I personally prefer a more stable software experience.
Not to say that the software is unusable in these Xiaomi, Oppo, Realme and simlar phones, far from it.