Using offsets in pads can be usefull, but they can also be abused.
The intended use of the offsets become more clear with an THT pad.
As you’ve already noticed now the offset moves the pad, but the “action point” stays the same.
In KiCad using multiple pads with the same pad number is a valid way to extend a pad.
Another way I just discovered is to draw some lines or a polygon, and then select them both in the Footprint editor and then [RMB] / Create pad from selected Shapes.
The selcted graphics become part of the pad, and you can view, edit, or delete them in the custom shape primitives tab on the pad properties:
(hover over pad) / e / “Custom Shape Primitives”
The best implementation for this would be an option to the Footprint Wizards for options to add Solder Thieves (for simple Footprints).
Really complex pads are probably best designed in FreeCAD and exported to KiCad with StepUp.