uBlock Origin + these settings make gmail very clean and distraction-free. It's also much easier to use for non-techies (parents, grandmas) with these settings:

[General] Hover actions: Disable

[General] Smart Reply: Off

[General] Button labels: Text

[Inbox] Inbox type: Unread first [see note]

[Inbox] Importance markers: No markers

[Inbox] Filtered mail: Don't override

[Chat] Chat off

[Advanced] Unread message icon: Enable

[Settings icon] > Display Density > Compact

NOTE: I find the [Inbox type] setting of "Unread First" works extremely well for myself and others, but this is a preference you will want to set based on the user. Either way, get rid of the multi-tabs!

My first thought was, here is someone technically skilled enough to modify the css of a page they do not own, yet they aren't blocking ads with an adblocker? I hope they did not waste the time on hiding the ads manually..

I know many SW engineers that will keep ads on as a matter of principle. They like to support the sites they use the most and believe that giving back in views/clicks is okay.

I'm with you but different folks different strokes!

That's what you have exceptions for. (whitelisting)

I use Firefox with noscript + ABP for general purpose browsing and default Chrome for Google-related tasks. I find that ads serve as a reminder to think about whether I should be doing something in Firefox instead.