While paying will likely not help your score, that is not the only factor. It is not simply a determination that if it wont help your score, you should not pay.
Paying will look infinately better in any manual review.
The reporting of a CO is essentially a statement by a prior creditor that you are expected to stiff them on the entire debt.
That is a killer in any consideration by a future potential creditor..... this consumer has a history of not paying their debt, and yet wants new credit.
By paying, you show that their determination that you are not going to pay did not, in fact, end up being the case.
You did pay when able, and thus you demonstarte that you do take responsibility for prior obligated debt.
A huge difference.
Settling for less is an in-betweener. You do attempt to discharge debt, but only at the expense of a loss to the creditor.
That is still an unfavorable portrait in future decisions, as creditors dont expect to take losses in their lending.
If you can get a creditor to agree to a settlement for less and also not to report paid/settled for less to the CRA, then it will appear the same to one viewing your credit report as if it had been paid in full.
