The Equity Index Account is a Russell 3000 index, basically the entire US stock market. It is absolutely a "true index". You do not need ANY other US equity holdings - this does it. The only reason to hold anything else is if some of your other options are cheaper. With indexing, of course, cheaper is better. CREF Global Equities sounds like it holds foreign stocks, doesn't it? The trick, though, is the word "Global". This fund is actually 60% US, 40% foreign. Do you have a pure foreign option in your plan? If so, what is it?
You might also wish to consider holding some money in TIAA Real Estate, TIAA Traditional and a bond fund. It does not have to be a lot. Owning more than one type of asset category tends to give you more return for less risk (as measured by standard deviation) over time. This concept is called Modern Portfolio Theory or mean variance analysis and won the Nobel Prize in Economics in 1990 for its originators: Harry Markowitz, Merton Miller and Bill Sharpe.
My recommendation is to schedule time with a TIAA counselor, whether over the phone or in person, and have them do an asset allocation for you. You do not want them to manage your assets - it's an extra fee. You just want them to give you suggested percentages, which you can tweak until you feel comfortable. Or you may have target date funds available. Each target date fund is a well-diversified portfolio in and of itself. Fix it and forget it.
As someone mentioned above, the TIAA annuity funds have an extra added kicker. For lack of a better way of describing it, you can build up extra points (they don't call it "points" but that's the idea) if you have your money in the annuities for a long time. That's something you can go over with your TIAA counselor. You can easily convert the annuity funds into a stream of income upon retirement, should you choose to do so.