Is a GoPro a good primary camera? I would say yes!!

GoPro's are extremely durable  and at the same time they deliver extremely beautiful images.
A higher image quality is not necessary for YouTube, Facebook or Instagram,
Because they will compress the image.  so there is almost no difference between a high end DSLR an a Hero 5 if you upload it. The DSLR will deliver better colors than the GoPro but you can do color correction to make the GoPro image nicer. If you have a DSLR you can change the lens and play with the zoom.  This is not possible with a GoPro!

So why to i think a GoPro is a good primary camera?    

- You don't have to worry about water
- It can fall on the ground without braking
- You can put it in places were you can't put a DSLR
- There are a lot of accessories available
- U can use 1 camera for every thing 

I personally use a GoPro for every thing because of those reasons.
I make videos of off-road vehicles and RC cars,  and there always is a lot of mud and rain and i think a DSLR won't survive for long. when i took a GoPro with my on vacation to the French Alps, it was awesome it is small it will fit in my pocked and i took it with my on every activity to make pictures and videos. 

And yes. the modern smartphones can record in 4k and 1080P 60fps    but put the video near a GoPro video
and you will see the GoPro video look better.

So if you don't want to buy anything. Use your phone.
If you want good quality an take your camera with you to a lot of different activities. Buy a GoPro.
If you want to make videos that have television/movie quality don't get a GoPro but buy something else