Wage and productivity are not as simple as that chart. Business invest in fixed/long term assets which employees in turn use to perform their jobs. Those assets increase productivity. The cost of those assets cannot be spent on wages. There has be an avalanche of new technologies that have become available in the last half century. For most businesses it is not a decision to invest in either employees or technology. Most businesses have to use technology to remain competitive. And of course, there must be employees to use that technology. How skilled the employees must be is dependent on the technology. Skill, knowledge and ability remain the determining factors of wage growth.
I don't know the percentages of skilled vs. unskilled workers are. Or, for that matter, what constitutes a skilled worker. There are plenty of people who use technology and are not anymore skilled than a trained monkey.
Regardless, more immigrants will at most just add to the trained monkey class of workers, but I suspect it would lead to more unskilled and unemployed immigrants dragging down average wages.
