It's pretty easy to debate from either side. The FS will shoot differently than the Shield...someone could say 2 FS will shoot differently from each other, and someone else could say; Don't we align the sights on all guns and then squeeze the trigger while holding the sights on the target...making the argument that we shoot every gun the same way.
It also depends on how much time you spend shooting and how many guns you own. If you own 50 guns, and shoot everyday, then you wouldn't be asking the question...it wouldn't even come into mind. If you have 2 guns, and want to have similar controls, because you don't get to shoot but once a week or month or every once in awhile...It makes a lot more sense.
Since you have already voiced the concern and desire to have both be more similar platforms, I think you've answered your own question.
I carried the G43, and it was fine, I could hit center mass no problem. Then I decided on a FS PC 9l, as a range gun, and I wanted similar platforms, so switched to the Shield. I absolutely love how the Shield fits me, and how I shoot it, and I can't imagine carrying anything else (Except maybe a 9c?).