Likewise, I think if you have a mouse on the right, then it would make more sense to have your nav keys on the left.
I'm not sure that I agree that arrow and nav keys would not belong on the right side. I use those keys mostly when I type, not together with the mouse. Otherwise I scroll using either the (right-handed) mouse or (right-handed) keys. Even if they would move, I think that the (forward) Delete key belongs close to Backspace.
I think that a staggered non-split QWERTY alphabetic area does not actually belong in the middle in front of the user but slightly to the left because of how the key staggering leans left.
When I sit straight in front of the desk with my arms stretched straight forward, my left hand is on the left keyboard half and my right hand is on the mouse. The arrow/nav cluster is not in the way at all.
And on the flipside, I disagree with you
. My custom is all about putting the nav/number clusters on the left for symmetry and mouse space, and getting rid of the key stagger centres everything. My use case is with nav/mouse interchangeably. I also put the backspace onto the nav cluster for the reason you state. In fact the reason I made my own is because TKLs were not doing it for me with no number cluster and with nav redundantly/uncomfortably close to the mouse.