Yes, it doesn’t improve the best mining score among the transactions in the example. It does increase the overall fees per vsize across the set of transactions we are examining. It depends on the size of the mempool and the overall position in the mempool of the examined set of transactions to determine which of those two are more attractive to miners. If there are few transactions available for mining, increasing the total fees may be preferable over a higher feerate transaction with a lower total fee.

What you are describing in the context of "highest minable fee-rate" is equivalent to the concept of mining score. If the (ancestorless) parent has a higher feerate, the parent’s mining score matches its own feerate as does the child’s mining score match the child’s feerate. If the child has a higher feerate, they share a mining score that falls between the parent’s feerate and the child’s feerate.