In Portland, we did similar combined sewer pipe. But they didn't size it to handle the largest rainfall. The sewers still overflow a couple of times a year, but it is much better than dozens of times. Especially since it now only happens in the winter when no one is using the river. It would have cost a lot more to handle peak rainfall. It is already expensive, sewer costs twice as much as water here.
Portland has also been working on the “next steps” pointed out in this article. Street bioswales provide absorption and holding capacity. Downspout disconnection programs and new build codes drain rooftop rain locally on the property or out to the street instead of directly in to the sewers.
I think we have an easier time due to our lower density. Most lots have decent amount of exposed ground for rain infiltration, and the area has well draining soil. Tougher for cities more tight and built up. I think Seattle codified water management before the latest building boom so hopefully they will do alright too!
Perhaps it was more expensive to modernise the sewage system and separate sewage from rain water, but what they done here does not fix the problem it just patches it so it's not a problem for now.
"It's cheaper to let someone else deal with this later" is not a good reason to not do something today. Why should later generations have to deal with this problem? What if they decide its their grandkids problem?
I'm sure there was a long debate on the pros and cons of different approaches here. I'm sure it's just the way the article is written, but either way it's annoying that we seem to lack the ambition to build things that last and that we can hand to our grandkids with pride.