There's upsides and downsides to complex and simple games. Fortnite may be simple in some aspects (basically a war game) but it's more complex than Temple Run.

Both cater to different markets but achieve simplicity within their markets well.

I don't think it is useful to think in terms of simplicity vs. complexity. Good design is about knowing what features work well together. Composition, harmony and efficiency are more important than minimalism.

I love lots of classic games like Contra which are at their heart very simple. But Yakuza 5 has everything from rhythm games to a little arena shooter built in and it's all optional content. A lot of it is kind of half-baked because it's so ambitious. That's kind of fun in its own way.