Interesting points as far as it goes, but many relevant factors are left out. Ok, wages rise faster, at least when compared to local cost of living. But generally, union pay is higher to start with. There’s less room for it to go upwards, so I wouldn’t be too surprised to see a slower increase, except possibly for a newly established union at a place with crappy pay. And this assumes his numbers are accurate, I haven’t checked that.
And wage/salary is not the only element of compensation. Benefits matter too. And union jobs typically have more and better benefits than non-union jobs. With the right benefits package, someone could easily be financially better off with a lower pay rate.
Also, aside from compensation, unions can also do a good job of things like training and safety standards.
I’m not saying that this piece is entirely irrelevant to the RTW debate, just that there are other factors that are very important in addition to speed of pay increases.