The brightness of each Hubble/Webb image is completely arbitrary, with the constraint that not too many pixels are oversaturated. With the exception of the Carina Nebula, the Hubble images you're using are darker than the Webb images, which makes the latter look brighter and "better." You should adjust the brightness of the pairs so that they are approximately equivalent, so that the comparison is based on the true differences between the images (resolution, ability to see further into the past).
The brightness of each Hubble/Webb image is completely arbitrary, with the constraint that not too many pixels are oversaturated. With the exception of the Carina Nebula, the Hubble images you're using are darker than the Webb images, which makes the latter look brighter and "better." You should adjust the brightness of the pairs so that they are approximately equivalent, so that the comparison is based on the true differences between the images (resolution, ability to see further into the past).