Hahaaaa :-)
Yes, SYS_INFO DOES return an average over all Processes so its not useful if you want the load of just one specific WP...
The only way I would know (which is one more of eternal workarounds) is:
parsing the WP logs for U00021601 and U00021602 which show the statistics per WP:
(sorry for the bad formatting)
20171023/152608.706 - U00021601 AVGR. 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 00:00
20171023/152608.706 - U00021602 'Client: 0000 00,16 00,00 00,00 00,00 00,00 00,00 00,00 00,00 01,48 00,14 00,16 00,15 00,16 00,14 00,16 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00'
20171023/152608.706 - U00021602 'Client: 0001 00,01 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,25 00,00 00,00 00,01 00,01 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00'
20171023/152608.706 - U00021602 'Client: 0003 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,22 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00'
20171023/152608.706 - U00021602 'Client: 0004 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,01 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00'
20171023/152608.706 - U00021602 'Client: All 00,17 00,00 00,00 00,00 00,00 00,00 00,00 00,00 01,95 00,14 00,16 00,16 00,18 00,14 00,16 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00 00,00'
the second only way that gets to my mind is catching the OS PID if every WP and use OS functions for getting the workload.