Are my drives being utilized equally with Linux Software RAID 0 array?
Solution 1:
The apparent bigger usage of the first device probably is an artifact of read alignment.
You have a 4x 512K chunk RAID0, meaning that the first device hits for any read aligned at 2 MB boundary. Both 2 MB and 4 MB are common alignment values for applications (ie: LVM physical chunks are 4 MB big by default), so the first drive can appear as more stressed than the others.
For a more in-depth (and correct) evaluation, you should observe your drives behavior during a typical real world test (or a reasonable approximation done via fio).