Overwatch isn't that demanding, you could probably do alright with a better videocard. The problem is videocard prices are kind of high right now. Something like a GT 1030, or older GTX 750 Ti, gives you an idea of what to look at.
The other problem is Witcher 3. That is both demanding on CPU and videocard. If you want to play games of that level then you will need the CPU/motherboard/DDR4 system upgrade AND a videocard to match.