No functionality has been removed.
As noted in the UI if you enable the enhance taskbar option you cannot centre the start button. This is unfortunately how that feature works.
You have two options to make it work how you like depending on your needs.
1) You can set the taskbar buttons to centre in Start11 settings which will leave the start button + widgets icon + search on the far left but centre the running apps + pinned apps.
or 2) You can go to the taskbar page in Start11 settings and disable the enhance the taskbar option at the top and then restart explorer. You will then be able to position the start button in the centre as you did with 1.11.