Your 'over-shrink then grow' method is a good one for ensuring the FS doesn't get corrupted when shrinking an LV. However the --resizefs option should be safe and quicker according to agk's comments elsewhere.
Re the "olden days" scenario: now that 2 to 3 TB external drives are very cheap, and USB3 or eSATA are very fast, you can simply backup all the partitions involved (a good idea anyway) to the drive, then repartition destructively and restore. (If you are using rsnapshot you only do an incremental backup since the overnight one, which will not take so long.)
This backup/restore model may be faster than doing the Gparted model of moving FSs to new location, as it uses 2 spindles not one. It also has the benefit of defragging your FSs - I know Linux FSs don't need defragging in theory, but in practice it will help somewhat particularly if FS has been in use for some years. (LVM's model will tend to increase fragmentation somewhat as you never do this sort of FS re-creation.)
I don't see why more than one reboot is needed with Gparted.