That seems very strange - it is as though the lower pistons are not operating with as much force as the upper ones.
The linked brake system means that when the rear brake is applied,
as weight is transferred to the front of the motorcycle,
the lower right piston of the front brake is partially applied,
so if anything, you might expect the lower right pads to wear out first,
but they look the least worn.
All pads for both discs must always be replaced together

After fitting the new ones I would take the old pads to your Dealer and seek their advice,
pointing out the difference in wear - measure each pad and compare then with new ones
to see just how much they have worn.
I'm wondering if there could be some air trapped in the calipers at the lower pistons.

That would result in a lower braking force being applied to the lower pistons,
and could also explain why there is less wear than might be expected on the lower right pads
as a result of the Linked braking system operation ??
The complete system needs to be bled properly - and needs to be done either by a Triumph dealer,
or with use of a "DealerTool" to open the ABS valves, and allow the linked braking system to be bled.
