/cast [@target] Light's Hammer

When I target another player the reticle appears at the cursor location (but does not cast). when I target myself Light’s Hammer casts at my location (without reticle). Is this an intentional limitation?

Yes. You can use @cursor to make it automatically cast at your cursor’s location or @player to make it cast at your feet. There’s no way to make it automatically cast at your target’s location.