I'm not sure I'm looking at the right monitor's specs when I study the details of your screen. From what I saw, and I may be wrong, the screen would appear to be largely for video gaming and movie watching, but there is a chance I'm looking at the wrong model. The screen I looked up doesn't achieve the full sRGB colour range, which is going to make things difficult for achieving correct colour. I would expect a screen which is being used for video or still colour processing to have at least a full sRGB prolile capacity, and preferably an Adobe RGB one. There are many monitors on the market which reportedly deliver this. There was a time when colour profiles weren't recognised by the browsers we use on the internet, but now three of the four do. To my eyes, the difference between them is quite striking.
The BenQ SW320 is a 32 inch screen with 4K resolution and Adobe RGB colour profile. It's delta is under 2, which safely takes it beyond most folks ability to discern. However, such specs don't always deliver what you might reasonably expect. DEL have something of a reputation for having some of their screens having a slight red caste on one side of their screens and blue on the other, despite them being 4k and meeting Adobe RGB capacity. It sometimes seems a matter of luck, if you believe the reviews that folk have written on B&H, Amazon etc.. Calibration doesn't fix this.
I use a Spyder 5 Elite plus for my calibration and it offers to calibrate different parts of your screen separately to achieve the most even luminescence and colour, if your monitor will allow this. I'm not familiar with either your monitor or the i1Display, but I guess that's the first thing I would be looking for.
It's not unreasonable to expect a delta <2 with a monitor built specifically for photography or video colour grading. However, this is usually achieved by the monitor using an internal 14 bit look up table to adjust the monitor's output. I wish I could give you clearer advice, but it's difficult when you don't know your monitor or the graphics card you are using.