I’ve had 4 Dell S3220DGF’s at this point, first one to replace a dead pixel and the other 3 to chase down getting one with 1440p120Hz support after the manual updated to indicate it now supports it.
I can confirm that myself and one other I recommended to get one, has gotten the 1440p120Hz option over DP and HDMI on the June 2020 Rev A03 models. This is not present on Rev A03 models before June.
The trade off, if you can call it that, is that the monitor no longer natively supports 144Hz as a refresh option within Windows. The options now are 60Hz, 120Hz, and 164Hz (165 goes to 164 after downloading and installing driver update from Dell website). I noticed your review still has 144Hz as native refresh option, but that is no longer the case as people will be receiving these newly built monitors with 120Hz out of the box and no option for 144Hz.
You’re right, they’re both very good TVs, but the TCL is a bit better overall. We’re in the process of changing our recommendations from the U6H to the TCL S555, but it’ll take a bit of time to get them all updated. We don’t currently have any plans to make a video comparison between them, but we’ll keep it in mind!