IMO, if you're within two years of your FIRE date, it's time to start setting up some cash flow for the withdrawals. You have to weigh the foregone potential appreciation in stocks against the risk of a crash either delaying FIRE or resulting in a sequence of return risk.
Personally, I've never been a fan of bonds and don't actually have any myself. Then again, I certainly called the last @20 years wrong -- interest rates have consistently dropped since I got married (my first house was at almost 9%), and every time they'd drop, I'd think, ok, that's it, they've got to go up now. My staying anchored to what interest rates were when I was growing up -- seeing 10-12% as "normal" -- meant I missed very significant bond returns. Of course, I still think that interest rates have to go up now, because there's not much lower they can really go. Because, you know, this time it's different and all that.
But all of that is the wrong way to look at it. You are not looking at bonds for return on investment, you are looking at bonds for return of investment. The nice thing about bonds is, if you buy a bond that is going to be worth $100 in 3 years, you know that 3 years from now you are guaranteed to get $100. At the one-year mark, it may be worth $50 on the open market; at the two-year mark it may be worth $150 on the market; but at the three-year mark you are getting the $100 you were promised. Can't say that about the stock market. Or bond funds -- bond funds can be mismanaged, buy high/sell low, overreact and panic in a crash, just like stock funds.
As I get closer to FIRE, I plan to set up a bond or CD ladder (depending on interest rates and such at the time). I will probably plan to have about 3 years' expenses in that ladder. So 3 years out, I will buy bonds/CDs equalling one year's expenses that mature in three years; then the following year, I will buy another set of bonds/CDs equalling one year's expenses that also mature in three years; etc. So that by the time I FIRE, I will have my next three years' income guaranteed, which gives me time to ride out any market dips without having to sell at a low.
Of course, you may not need this level of security -- you may have a backup plan to tighten the belt, go back to work, whatever. But for me, since I am going to be close to 60 and may not be able to find work, it's important to have adequate protection for my downside risk, even though it means giving up some of the upside potential.