For what it's worth, I'm not sure I've seen much I could objectively call sexism either. Some, but not a lot. Certainly not enough to use words like "systemic."
One explanation for this is that it isn't happening. Another is that it isn't happening in my "spaces" (networks/companies/etc.). But another is that it is, but in ways that I don't see. I don't know how much all my coworkers are paid, and if someone is receiving unwanted advances it would likely be happening where I can't see it. There are other explanations too, maybe I'm used to some sexist behaviors and wouldn't notice if they happened right in front of me. A lot of the tech culture humor I'm aware of, and have participated in, revolves around programmers being men. It took some time and some serious reflection before I realized this was the case, and that it was a problem.
So sure, no one in my office runs around "grabbing women by the ...," or joking with me about it, but that doesn't mean sexism isn't happening. And I respect and trust my female peers enough to take them seriously when they tell me it is.
All that said, there's one piece of data I simply can't square with "sexism isn't a serious problem in tech." Every company I've worked for, every conference or meetup I've attended, most of the blogs I follow and books I've read - vastly more men than women. To the point that it's almost absurd. Here's what gets me about that - I love what I do! Tech is a great field to be working in for a ton of reasons! Objective reasons! On top of that so much of tech lends itself naturally to inclusiveness. What the fk is going on that I can work for years on teams of 90% men?! This doesn't prove sexism in tech, but it's evidence that something is up, right? And the accounts I've heard of women being treated poorly in tech give credence sexism as one possible and reasonable explanation.
Heck, I don't even think I'm arguing with you. Your posts sound reasonable, I get the sense you care, and I'm certainly less familiar with European tech culture than American. BUT it is worth your time to dig into the, "if I don't see it isn't happening" thing because that can be a trap; one I've fallen into myself.