Sewage doesn't have to be dumped. Simply separate your black water and grey water. Storm drains can go to rivers (if the rivers have capacity – if not, it's sometimes easier to give the river more capacity than to build more sewers), and the amount of water in sewage pipes will be independent of the amount of rain.

Sure, the sewers might not currently be designed that way, but that can be changed. (It's a logistical challenge, but it needs to be done.)

This is such a pedantic point.

How does it add anything to the conversation?

If a sewer system can be designed such that dumping sewage need never occur, you can earmark some of the budget for gradually introducing this property into your sewer system. The more such improvements you make, the less often you'll have to dump sewage, until you never have to. Thames Water could have done this.

We already know that more things can be done, in a better way, etc., if given more resources, more time, better decision makers, etc.

That’s true for all organizations.

Aye, the fact that the WHOLE system would cost trillions to upgrade doesn't stop anyone from upgrading it slowly in this way. The problem will still exist in 50 years, any progress is better than none.