It is, though it's more the overall culture it has created than online dating itself. The culture where there's always more and better options so you shouldn't commit to anything, where cancelling plans is just a text away so nobody takes them seriously. It's infested even non-dating relationships and is quite confidence destroying to have people cancel on you constantly.
Also, when I changed genders the dynamic did shift a lot, but it's still confidence destroying. As a male-identified person it was very hard to get matches and the whole process was a tremendous amount of work. As a female identified person (though still dating women) the number of matches I have is basically infinite. Most of the other steps are easier too, though it is still a fair amount of work to get someone to show up. But when they do, it's rare to find people looking for emotional intimacy. It's much easier to wind up feeling used (as an experiment or otherwise). Queer drama is crushing in its own unique way.
Even if you are reasonably attractive and desirable, people still want to invest the minimum, play the numbers game, and not commit to anything. Even if you're 90th percentile, that still means 1 in 10 are more <insert trait here> than you, so you can keep re-rolling; why not? I'm absolutely not immune to doing this myself; my standard for "Someone for tonight" is worlds apart from "Someone to have a relationship with", but it's not exactly like I'd disclose that up front, even if I immediately know what category my date is in.
After watching over my single-mother sister's shoulder while she used her okcupid account, I highly doubt it's anywhere near as confidence-destroying for women as it is men.
For her, she could login to okcupid any time she wanted an ego boost. She was constantly barraged with messages and likes, it was a completely different experience for her to login vs. me. I didn't even know those notifications stacked up across the screen, for her it was a maelstrom of attention.
Likes are cheap; they literally cost nothing. So are message that say "hi", with no indication that they've even read your profile. Logging into a dating app and discovering thousands of people -- all of whom seem to know only that you're female and therefore approve -- is as soul-sucking as getting no attention at all.
I was very popular on online dating sites, because I knew how to talk to women as if they represented something other than a place to put my dick. All of the women I spoke to were incredibly discouraged by quality of attention they received. Ask your sister what fraction of those stacked-up notifications consisted solely of the word "hi".
Most women seem to get tired of the attention that merely tells them that they're attractive. It's an ego boost for a while, and I'm sure some retain it, but it's the kind of thing you get inured to, and you want something else.
The experience for women is different, but not necessarily better, and the things that a man might crave simply because he doesn't receive it will feel empty to a woman precisely because she does. There's a cultural asymmetry that doesn't lead either side to what they're after. But men can do a lot better simply by treating women like human beings, and understanding that they've got problems different from yours.
We ended up discussing her dating experience at length at the time. Honestly it was plain ridiculous. Sure, many of the OKC messages were short "hi" or other thoughtless one-liners. But the content didn't matter, she treated them all as signals for a live one which drew her to their profiles where she would then hold a little impromptu trial of eligibility based on their photos and profiles. Most of the time she wouldn't respond, and it had nothing to do with the content of the messages. It's the photos, age, race, married/divorced status and religion that matter to her. The message notification just made her look.
What I saw was the polar opposite effect to "confidence-destroying". She became increasingly superior and picky with all the interest. And when she did go on real dates, she would find the smallest flaw as fatal because she had the impression that there were an effectively unlimited supply of competitors.
It does sound as if she got "gamified", taking pleasure in the app giving her pings. Such things afflict most of us in one way or another (including me). I suspect she'd find it more satisfying to seek out thoughtful men who are interested in her as a person -- but like I said, she should do whatever she wants.
My understanding of women's take on dating apps is, of course, heavily informed by the fact that they were usually dating me, and selected for that.
One of them said that for some women, it was pretty good if you like incoming messages and interest.
But for the other women, it was horrible because you'd get ignored, except for those weird cock shots most women get, which adds a bit of creepiness to make the experience worse.
Basically, women are sorted into attractive and unattractive by whatever arbitrary standard of the day, and the latter cohort had very little interest.
The statistics also indicated that skin colour made a big difference.
Can also confirm that online dating is a horrible, confidence-destroying nightmare (presumably for both sexes).