I review about ~100-200 CVs per week in bulk, for Data Science.

I actually treat a cover letter as a negative signal. Who has time to write one, and why you do think anybody cares? Show where you worked, what you did, link to some interesting stuff, all this in the regular CV structure, and that's it. I have about 10-20 seconds per CV, reading a cover letter is out of the question. The only thing the CV is for is to (i) send some signals to pick out the 5% of applicants that make it to the first screening round, and (ii) at later stages, to quickly open it to recall who the applicant is.