I found a fix that doesn't mess with the scaling or appearance.
Locate Gw2-64.exe
Open the folder bin64 within the same directory
Right-click CoherentUI_Host.exe and select Properties
Switch to the tab Compability and Change high DPI settings
Check the second checkbox ("Override...") and ensure that Application is selected in the drop-down
Close all windows by clicking OK
Apparently the executable that's hosting the CoherentUI doesn't work well with DPI scaling. Luckily it's a seperate executable and only hosts, not actually displays any of the UI, so the scaling of the main Gw2-64.exe is still applied.
I noticed however that closing the launcher or the client without having started the game by selecting a character can reset the account name.