Ultra Wide lenses are harder to design because of the low angle at which the light hits the sensor. There will be a lot of distortion correction going on as well. This correction ends up smearing the extreme edges or final third of the image. Improved lighting will improve contrast which in turn gives the impression of sharper images. Lower light will reduce contrast and require a higher ISO which will have a detrimental impact on image quality.
As a photographer, I spent over £2000 on an ultra wide angle lens (10-24mm Full Frame) rather than £800 because the optical quality for £800 doesn't buy edge to edge sharpness, you'd still have softer edges etc. So, to expect a phone to produce Sharp images edge to edge on a UWA is probably unrealistic, even with a small sensor and increase depth of field it offers. I don't have the phone myself (still prefer my iPhone X), so I can't comment on how good/bad it is.