This is actually impossible to predict. It depends on how your ISP is connected to other ISP.
The theory is that IF you can get a very good connection to WTFast data center they MIGHT have a better path to the game server than your ISP does.
The place this works best is in asia. A lot of this area of the world is connected via undersea cable. Not all ISP have access...ie are willing to pay....to use the most direct fiber connections. Smaller ISP only have so much money and they may not buy the ability to run traffic on all the different connections. So they might have good connection between some counties and not others. What you hope is using WTFast might have traffic that uses different fiber connections.
This...