To me, it seems slightly silly to pull one aspect out of a training system and analyze it by itself. Nit picking at speed work (in this sense, not plyometrics) while ignoring other characteristics of "Westside" training is a bit much. If one simply adds speed work into their current program, when they aren't following the principles of the whole training system, it probably won't work well.
I'm fairly certain that the percents most people use when doing their "speed" work is grossly reduced compared to what is actually used by members of Westside. Some of their speed work is heavy as fuck when you add in the accommodating resistance. Hell, if you're not using accommodating resistance, you should be using like 70%-80% of your max anyway, which is still pretty heavy.
Lastly, I don't think the Mike T article is even really disputing ANYTHING about the training system that speed work is involved in, but simply stating (with empirical evidence) that the force produced through lower percentages is not actually as high as the force produced through higher percentages of your 1RM.
PS: On a personal note, I didn't see many gains at all through Westside principles as a raw lifter. However, there are many who have, and there are many who have had those gains DRUG FREE...So don't start that lol. I personally don't believe it's an optimal system, but I tried it a long time ago, and I think I could make it work a lot better now.