I appreciate that it's a little annoying and repetitive, but I think in this case, it really is better, because the business logic for exactly what should be do

I appreciate that it's a little annoying and repetitive, but I think in this case, it really is better, because the business logic for exactly what should be done with each value in the case of a conflict can vary so widely. It's good to have the full flexibility of SQL and all of the associated values to work with for the purpose of constructing the new value for the column.