That is indeed an issue and I see your point!
However, I think the root cause of the issue is the attitude these people have in general. So, just removing screenshots won’t make them suddenly think about such topics.
On the other hand, adding the most beautiful app still won’t work if their favourite proprietary what’s it’s name Facebook integration is missing, beceause F-Droid tries to focus on FOSS apps and apps with such integrations aren’t first class citizens.
One would need to fix the people and their attitudes. This can’t be done by limiting the F-Droid store, to, for example, being less convenient with screenshots.
I personally use F-Droid, because I think about such stuff and I care about privacy, but mostly about security, which is naturally implied from open source software. I still want to see screenshots, because that’s the best and easiest way to transport information about how the app seems to work. (Videos would be even more accurate, but that again takes longer to deliver, so pictures are the best middle-ground.)
That said, pretty pictures just remain pretty, as long as the app is downloaded and actually holds to that promise. If the app downloaded is not as pretty or useful, it’s an even a bigger disappointment to the user.
Additionally, a lot of proprietary apps indeed have a straight up better UX, than free alternatives. Of course, that’s not always the case, but more often than not, if comparing free and non-free apps with the very same purpose and goal.
For consumers, it’s often a question of caring about privacy or security vs. having the best UX. And just because the former seems most important, it does not allow for UX capabilities to be simply ignored or toned down.
UX is extremely important. The best app with the best features on earth will be absolutely useless, if (almost) nobody is able to use it.