Retro pear - so you think my DCs aren't being challenged because of one app I highlighted in response to a question about apps for a 2yo? Not too many assumptions about a stranger's home life going on there, jeez!
If you saw the use that Lego, for example,is put to in this house you would realise that they are way more advanced than that particular app in pattern recognition, and indeed both hitting targets above their actual age.
I used the ice cream app as an example of an app that has educational use from age 2, but that is fun enough that my 6yo still gets pleasure from it when he fancies it. And even if it is simple, it is reinforcing pattern spotting techniques. Watch my 3yo doing a 'spot the differences' picture in a book (yes, surprisingly we do have paper in addition to screens!) Just because she is way more advanced than that app doesn't mean she can't do something simpler when the mood takes her. Same for my 6yo.
I read Harry Potter as an adult and read trashy mags a fair amount despite having a degree from Cambridge which means I have the training to challenge myself with quite complex intellectual ideas. I do simple mental arithmetic and puzzles for fun despite being part way through an OU maths degree. Adults are allowed to challenge or not challenge themselves as they see fit depending on whether they want to learn or relax. Are children only allowed to do things that are challenging them with everything else being a waste of time? Wow, what a fun-free hot-housing mindset you have! There, that's me making an assumption back about you 
Right off to read some books with my
3.6yo, who will read some of the words to me, because she is bright and given a variety of opportunities to develop by me. And is clearly undamaged by a little bit of screen time.
Oh and some books are shit. I'd rather my DC had a good app over a crap book any day.
As I said before, and will say until I'm blue I'm the face, some focused controlled thought-out screen time is unlikely to damage a 2yo or older and indeed is likely to enhance their learning and skills.