We could have said this about XOM a couple years ago. Look where it is now.
This is where skill really matters.
Index funds have allowed me to not have to save for retirement anymore (have enough based on FV calc), and yes buying the FAANG stocks 6 years ago would have yielded much larger returns, but could also have yielded losses if they went the way of Exxon.
However adding some money into the market leaders would be a wise idea IMO. I.e. TSLA and AAPL. Since you are in the ETF ($SPY) for now then you are already invested in AAPL as it's the largest portion of it so adding TSLA which is going to be $5,000 in a decade would be wise.