RE: Which GP features have been missed on the GP 2018 Web client compared to the desktop client?
I've seen some customers that used the 'original' web client from 2015 (which was Silverlight based) be very disappointed when they upgraded to the HTML5-based web client.. in the old one, you had somewhat a feeling of GP that merely looked like the fat client.. not so much anymore in the HTML5 web client, which aside of all the cons that David mentioned, doesn't allow to move / toss windows aside to see other windows content.
In order to get multiple windows open from the same company in the web client, you need to login multiple times by opening multiple browser tabs or windows.. That is the only benefit of using the web client, as it counts only 1 license for those multiple 'logins' into the same company.
Other than that, I don't see any benefits of using the web client, as it's clunky and very limiting. You can't even use any keyboard shortcuts that fat clients are used to, because those are intercepted by the Web browser and interpreted differently...
There are more cons than pros on the web client and many customer I know just decided to ditch it.