"While construction unions are backing this project, labor disputes could also get in the way."

Some union dispute indeed delayed the start of the tunnel by a month.

On the other hand many of the cited possible problems might have been amenable to fixing in place, e.g. the cutters in the front are replaceable. The terrible problem now is that its main bearing is messed up (forget if it's just one or more seals, or worse, or even if they really know yet), requiring this major excavation to get to it and then surgery. If the problem wasn't, or wasn't uniquely caused by that steel well casing, it could get broken again ... it's only done 10% or so of the length.

And, yeah, the traffic projections aren't great. As I remember, no matter how people go "wow!" about the size of the tunnel, the capacity of it will be quite a bit less than the viaduct. Then there are all the other factors that can make it less desirable.

The Stranger has a long history of fighting losing fights to keep things more-or-less the same -- unless the alternative is trendy and/or guaranteed not to impact Capitol Hill. For example, they'd prefer that the viaduct be replaced with a "surface boulevard" that has a fraction of the throughput, thus all but guaranteeing decades of gridlock in downtown Seattle (which they like because it "discourages driving", because they heard that San Francisco did it...and most importantly, because it doesn't affect their lives either way).

Meanwhile, they complain constantly about light rail on the hill, but they campaigned heavily for the monorail-to-nowhere. Why? Because it was a monorail (cool!), and the construction wouldn't affect their favorite neighborhood (even better!)

Point being, it's not difficult to pull an article from the Stranger predicting doom for a major urban planning initiative. That's practically their stock in trade.