FanGraphs has league average positional splits going back to 2002. Here is the link for league average at SS...
https://www.fangraphs.com/leaders.aspx?pos=all&stats=bat&lg=all&qual=0&type=1&season=2021&month=38&season1=2002&ind=0&team=0,ss&rost=0&age=0&filter=&players=0&startdate=2002-01-01&enddate=2021-12-31&sort=1,a
Pretty interesting that from 2002 until 2017 league average wRC+ for a SS ranged between 87-92 every year, then starting in 2018 it jumped up to 97, 100, 102 & 99 over the last 4 years, so it appears the offensive bar for SS has risen somewhat from the historical norm.
If you want to see how league average offense has evolved for some other positions over the same time frame just make sure to change positions via the "Split" drop down menu vs the positional tabs above for the most accurate results as the positional tabs include all players that played those positions (even if only on a part time basis) while the "Splits" drop down menu option isolates contributions at that specific position.