System Files on MacBook Pro taking up too much space

I recently checked "About this mac" > "Storage" and found that the "System Files" are taking up almost one third of my SDD on this high end macbook pro (256GB out of 1TB flash). I think this is too large for an OS. Is Mac High Sierra 10.13.4 really 256GB????

I use "Clean my Mac" software regularly to clean out junk. So where am I going wrong and how do I get my "System" folder or group of files down to a reasonable size?

Please help, thanks!