I'll share my perspective on brightness and a little more after owning both the 2017 MBP Touch Bar (512gb model) and 2018 MBA (256gb model).
I prefer the MBA because of form factor (much slimmer look from the front), color (gold), and longer battery life. And yes, to me, looks of the product matter. The weight may be only .25 lbs difference, but when traveling the adaptor also is much smaller for the MBA which fits better in my slim Tumi case on the go. However, I would not have made the switch if the MBA did not have the fingerprint reader like my MBP. As for space (I went down from 512 to 256), I use iCloud, so I have over 200gb still free because it doesn't actually download all the files on your computer unless you actually click that particular file. So they all appear to be there, even though they aren't. I do notice slightly less performance in daily tasks of maybe 10%, but it doesn't bother me as much as seeing a thick bulky computer all the time (even if the weight is close).
Now for the brightness comparisons:
At first, it does seem the MBP screen is much better when you compare them both at full brightness. But when you keep the MBP about 2 notches below from the max, it is pretty similar to the MBA screen (kept at full brightness) to me in terms of brightness when at home or in my office. Based on posts by various members here, I was concerned the brightness would be much worse (especially 300 vs 500 nits, etc.). If you keep your MBP at 2-3 below max brightness, it is my personal opinion that there should not have a brightness issue if keeping the MBA at max brightness. Again, I compared both my computers side by side in an indoors setting with lots of lighting.
As for colors, the colors look much better on MBP when that's at max brightness, but when you compare the laptops at 2-3 below on MBP with max brightness on the air, then it looks pretty similar to me from color quality as well. I received my MBA on Nov 7, but I didn't get time to actually set it up and compare till this past week.
But we're not talking about the Macbook Pro. We're talking about the 2018 Air. And the 2018 Air is, without question, dimmer and more washed out than the 2013 Macbook Pro. I know, because right now my main portable is the 2013 Pro. The 2018 Air is nowhere near as bright when maxed out.
Also, there are valid questions whether the 2018 Air truly has a 300-brightness screen; some reviewers have measured significantly lower levels than that on the 2018 Air. There are additional questions about different panel suppliers and quality levels.
Bottom line, I've seen the 2018 Air in person. Anyone with Macbook experience instantly knows the 2018 Air screen is dim and dull. Until you actually examine one, you are in no position to conclude the issue is "hugely overblown."