Originally Posted by
fulminating
I don’t think it is that irrelevant - reattaching bits of the same soul seems to have affected density far more than strength for instance. Formerly ryne until the retcon, the wol, graham and potentially krile are all at 9/14th and not notably stronger than other denizens of the source - or more pertinently the first, ninth and thirteenth.
Taking the two souls thing literally, blessed siblings do seem to stand on a higher baseline than one souled people. Similarly zarol ja, mr snakes from vanguard and the arcadion fighters all seem to get notably stronger wearing a foreign soul. This does seem to also have some pretty bad side effects such as killing you and needing souls to use. I think zarol ja is the only individual we see fight without, with an extra and with a lot, so the main source of extrapolation about how much impact it might have.