What games are you playing?
Most games are heavily single-threaded.
This means that they are only able to fully utilize 1-4 cores of your CPU. This is why your processor is only at 30-40% load, as the game is not optimized to efficiently use all of your 8 cores. This is completely normal behavior.
For example; 3 of your cores could be working super hard, at 90-100% usage, but the remaining 5 are not being used, leaving the TOTAL CPU usage at only 30-40%.
The Ryzen 7 2700X's single-threaded performance is nearly identical to a Core i5 6600K, so many CPU-intensive games should perform quite similarly. (seen here on Userbenchmark:
https://cpu.userbenchmark.com/Compare/Intel-Core-i5-6600K-vs-AMD-Ryzen-7-2700X/3503vs3958 )
Sadly, unless a game is designed from the ground-up to utilize all 8 of your cores, the 30-40% usage is very common.
So yes, this is normal behavior, hope I helped you out.