The articles points to the statistical probability of winning more points if you hit your 2nd attempt like a 1st serve. But, I noticed when they interviewed the players that did not agree with the theory.
I think the common sense approach is to work to have a good 2nd serve that is not as fast as your 1st serve but goes in 90+% of the time.
If my opponent is a good returner, I will attempt a faster or more aggresive placement on a 2nd serve but I will not hit every 2nd serve like a 1st serve.
I have never played anyone or seen any good players who hit both serves like 1st serves either.