I'm in a very similar position to you OP, I have a 16GB/256GB 2014 15" MBP with integrated graphics. I thought I'd pick up a 8GB/256GB Air just to try it out before parting with my 2014 Pro:
- The form factor is a delight. So light, easy to open, solidly built. I know I'm coming from a 15", not 13" so some of this probably won't be as big of a shock for you
- The Air's screen looks noticeable crisper, even set at the higher scaling option
- Brightness is similar on both panels
- The 2018 keyboard is a nice improvement over the 2016 and 2017 MacBook Pro keyboards. I got used to it really quickly
- The force touch trackpad is much nicer than diving board style of the 2014 MBPs
- Battery life is awesome. Definitely an all day machine
- Never heard the fans spin up, even though the CPU usage would sometimes be quite high
Anyway onto the performance;
- For normal tasks, a couple of Safari windows with 10 tabs each, Pages, Mail, etc, it feels nice and zippy
- Once adding a second browser (Brave) running Google Docs and YouTube, things got a little less responsive. By that, I don't mean laggy, but more the system hesitates for a fraction of a second after you click something. It was only at this point did the memory pressure graph turn yellow
- The CPU usage sometimes got quite high when Mail or Dropbox was doing various things in the background. This isn't something I was used to seeing on my MBP, but didn't seem to affect actual system performance
After a week of usage, I reopened my MBP and it felt more fluid than the Air. Apps would launch about 0.5-1 second faster, or about one dock bounce less, and there was less hesitation in things like full screening an app or app expose. Even scrolling down Facebook rendered parts of the news feed about a second quicker on the MBP than the Air. That probably is due to it having 16GB of RAM and a slightly better iGPU even though it is older.
So I'm not really sure how to conclude, since I'm not entirely sure myself. I think without comparing it directly to my MacBook Pro, I'd probably be really happy with the Air, the list of things I liked about it is genuine, and I certainly recommend it for the casual user. It's what I recommend to all friends and family where I know their usage is typical.
However knowing myself, I like to have a lot of things open, and sometimes my work does require an additional browser open. Given I managed to get memory pressure to yellow through legitimate usage, I'd probably opt for the 16GB model since I don't want to change Macs 1-2 years down the line.
Since you mentioned you use Lightroom, I'd probably advise you do the same, especially given the Intel graphics shares the RAM.