I can agree with that. But I could say that about things in Windows and MacOS too. It's not like Gnome is unique in this regard. In some regards Linux is more advanced than Windows or MacOS, does that mean Windows and MacOS users are "used to mediocrity" as the article says?
As for not wanting to upload the wrong one, doesn't the file picker show a preview of the selected file? Sure, not as good as thumbnails, but it should be enough to avoid the problem.
I do say things like that about Windows too, and I back anyone who writes a blogpost excoriating Microsoft for their longstanding faults. As a long-time Windows user I can definitely say I am used to mediocrity in many areas. Thankfully no longer on a daily basis :-)
Some of the GTK filepickers on my system do show previews (e.g. Signal) but others do not (Mozilla - since fixed by the incantations needed to have them use KDE's).
As for not wanting to upload the wrong one, doesn't the file picker show a preview of the selected file? Sure, not as good as thumbnails, but it should be enough to avoid the problem.