The faster your RAM is, The faster your RAM can transfer data to the CPU which then transfers that data to the GPU. Slow RAM can disrupt the harmony of your parts and create a bottleneck that lowers your FPS in a significant way, but upgrading RAM won't magically increase your computer's performance by huge numbers, your CPU and GPU comes into play as well, as far as I can see, your CPU is much more weaker than your GPU - RX 470 which can cause limitations when your CPU can't keep up with your GPU which results in your CPU bottlenecking your GPU, but it's kind of common thing to see in Older "Pre-Built" Computers.
You can't really blame that people are roasting your rig, it is old, it is indeed very old, I'd say your RAM is little too slow as well even for DDR3 system.
Sure, your rig can run the game, at some extent but you will struggle in areas, as your struggling now, I'm surprised that you find your FPS as playable in Raids, but then playable FPS can be subjective for different people, for instance back in UE3 times, most of people found 10 FPS pretty playable,
Long story short, you should upgrade regardless, I don't know what your situation is on why you are still playing on an old computer, but it's time to move on, onto something better, as years go by, your rig starts failing even more as it won't keep up. If your budget does not allow the upgrade, than you have to simply deal with the cons that it comes with when gaming, there is no point in you trying to investigate and search underlying cause so you can magically boost your computers performance, the problem is clear, you know it, I know it, everyone knows it.