I have a strange feeling that off-index industry stocks represent an interesting view into the market. In particular, non-FANG tech stocks. Microsoft is a huge tech company, has been around basically forever (for tech), and its stock has been doing well – which I think says a lot more positive things about technology than tracking Facebook, Amazon, Netflix, and Google.
Partially because some of those companies have super specific issues that don't really reflect on "tech stocks" as we mean the phrase, whereas Microsoft is a tech supplier and measures the industry much better. But also because, once someone puts a group of stocks together, like FANG, says it's high-return, and waits for the cash to roll in, those stocks tend to really burn through a lot of upside potential.
Without looking at the data, I'd anticipate S&P500 stocks to have experienced more growth in the past 10 years, but also seen more correlated returns, than the Wilshire 5000 – if there's any substantial difference at all. Just because, at the margin, you have index funds – people investing based on the group the stocks are in, and that's it. And that should create correlated returns.
I'm sure financial products exist for in-industry-outside-traditional-indexes. But that seems like it would be mostly small-cap companies. Tech in particular is interesting because, with companies like Uber staying private much longer, we could have investment devices for large-cap off-index companies in the near future.