So, are there any reasons left to pay more for a smartphone?
Yes.
People who care about features.
OnePlus Nord: no quad HD display, no headphone jack, no micro sd card, no IR blaster, no desktop mode, no ip68, no wireless charge, no Hi-Fi dac, no dual display option, no 3rd party accessories, questionable pen support, questionable reliability, average cameras for the price, 2MP macro camera that's basically unusable, plastic build.
So for 399 EUR, people aren't going to spend their money on such poor option when the iPhone SE 2 is about 100 more. Those into Android will most probably go towards the Samsung A series route.
As for the price in the USA, OnePlus has completely rendered itself irrelevant, because for $100 more you can get the widly acclaimed LG Velvet in stores that features most if not all of the features above, in a premium package, with way better cameras and a silky smooth UI.
OnePlus' marketing team, we've had enough of you.