I'm assuming that you made the changes in essbase.properties file under <epmdrive>:\Oracle\Middleware\user_projects\<yourinstance>\aps\bin
Did you restart the services after making the change?
Yes the service was restarted after the change
I tried it at my end and I'm using 18.104.22.168 and it is not showing an option "Create Smart Slice" for a read user. (even though the property file says so). If I make him Database Manager then he get the permission to create one.
Try logging an SR with Oracle.