It is probable, that Your card's video ram is not enough.
If it is 2GB version, You should lower game settings to adapt to those 2 gigs. If there's not enough vram, You will experience frame drops and screen freezes.
4GB might be not enough as well for a high level of details (ultra)
At first, get a new GPU. New RTX2060 is a good choice. Or You can buy used 1080ti if You find a cheap one with a warranty - that's also an option (a bit risky though).
If Your budget is limited, used GTX 1070 should do the job for games such as Rainbow Six and Fortnite.
You should see significant improvement over RX 460 after this upgrade and that might be enough to deliver a comfort gameplay for You.
If not, You can find a cheap 6700k somewhere and overclock it a bit with some good cooling. (Your old cpu can be sold for a part of the money You spend on i7) - that's what i would do in this moment. I think 6700K at 4+Ghz should last for a long time.
The other option is a brand new platform BUT Ryzen 5 won't be faster in games than overclocked i7 6700K and probably You'll spend more money on it.
However, r5 2600 is still a good choice, while You gain DDR4 platform, which might be upgraded when ryzens 3rd gen will come out.
EDIT: OH, totally forgot.....8GB of RAM is not enoug in 2019 ;-) Check, how much RAM Your games are using. First comes GPU+additional 8gb of RAM, then You go for CPU if necessary. You can borrow DDR3 from someone to try it out first - the difference should be noticable.
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