you're not factoring in a few specific things:
1) how many of these people leave the country in this analysis.
2) OPTs likely will get h1b/l1s/leave the country and are being counted distinctly.
3) not all h1b/l1/OPTs are for tech. majority for sure, but there's a conversation factor.
specially in the current situation that green cards are much harder to obtain and many OPTs don't find a job, I expect 1 to be much larger than in the past.
as a more general observation, this line of reasoning does fit lump of labor fallacies: https://en.wikipedia.org/wiki/Lump_of_labour_fallacy
Oh, there's a name for it! I've sometimes been struggling to verbalize in the past the logical issue I perceived with the "immigrants steal are jobs" absolutists, and this is a useful reference.