How to reset Launchpad order in macOS High Sierra?
At the moment, it seems there are two answers to your question. The one answer is exactly the method you've laid out above (or the equivalent of removing the database at /var/folders/). The other option is... you can't.

With High Sierra, most - if not all - flash storage-based Macs had their file system upgraded to APFS from HFS+. Now, I haven't exhaustively read Apple's documentation on APFS but there is one item in the FAQ that sticks out to me which reads:


  Calling readdir(2) on a directory in APFS returns filenames in hash order, whereas HFS+ returns filenames in lexicographical order.
  [Source: Apple Developer Documentation]


The defaults trick technically still works. On HFS+ disks in High Sierra it still works as expected (tested by myself). On an APFS formatted drive you can see that it does something in that it resets the order but just not alphabetically. The order, then, is most likely arranged by the hash of the apps' names and not by the names themselves.

The solution for APFS? All I can think of right now is using a database tool to manually sort the entries in to alphabetical order. But then again, might as well just drag and drop...