Every aspect of the HHKB Pro 2 seems perfect to me. The key placements and lengths are just fine.
I use the Right Shift almost exclusively in preference to the Left Shift, and the size of the key is ample. I have used keyboards with a Right Shift of 1.25 u, and this is still fine with me. However, I have also tried keyboards with a 1.00 u Right Shift, and I find this too small.
As for Backspace, I assign the key immediately above the Return/Enter key as Backspace, and this works perfectly for me.