If they were all like that surely it would be plastered all over the Internet and in reviews.
Not necessarily as both monitors are new, likely only shipped to a relatively small user base and of those using the monitors not everyone will be using VRR (G-SYNC or FreeSync) and even if they are then they may be using settings or framerates in specific games that is a non-issue for them. Many will possibly not notice it if they are using it in a bright room as opposed to a dark room, which is how I do 90% of my gaming so the flickering is hard not to notice.
Also, the professional reviews barely cover VRR in any depth, only mentioning if a monitor supports FreeSync and/or G-SYNC. The majority of them almost certainly do not test games properly. At best, they'll load up a few test games, check VRR works, put a tick in the checkbox and call it a day. It's the users that report these kinds of issues over time and from what I can tell from researching this issue there are a lot of forum posts from people reporting VRR flickering with OLED and QD-OLED displays, not just the Dell monitors. The question I have though is this flickering actually worse on the Dell monitors than other manufacturers because I have no way of knowing as this is my first OLED monitor. However, I have seen some VRR flickering in PS5 and Xbox Series X games on my 2019 LG B9 TV but not to the degree that I am seeing on the AW2725DF monitor. Then again I am sat much further away from my TV and it maxes out at 120 Hz.
My monitor supports 360 Hz so with technologies like NVIDIA's DLSS3 frame generation I can play games that have highly framerate variance because that is how this works. I bought a 360 Hz monitor not because I play competitive online games (I don't play any) but because I wanted to take full advantage of frame gen on my RTX 4080 as on my previous 165 Hz IPS monitor frame gen was capping out at 158 fps. Frame gen works brilliantly on this display, I can play games like Dakar Desert Rally at 180-240 fps with frame gen but these sort of games are more prone to showing VRR flicker.
I can't even use Fullscreen + Windowed for G-SYNC on my monitor, only Fullscreen, because if I do then I get a lot of flickering on the desktop wallpaper and this gets even worse if the taskbar appears or I open a window (on the desktop, not in my house!). As such, I am forced to use Fullscreen only for G-SYNC which means that any games that run in window mode will not use G-SYNC. It's a bit of a mess really. I really wish I had known how bad this issue was before buying the monitor because it is really the only thing I dislike about it. I play lots of games and rely on G-SYNC so I can max out the settings at 1440p on my RTX 4080 without worrying about judder or screen tearing.