What you describe is exactly the problem I have with index funds. I manage a decent amount of money through Vanguard. The index funds in my portfolio fell less and recovered sooner, but at the cost of raw gains. The managed funds I have basically fell apart because apparently the fund managers are idiots who didn't even try to keep up with market trends. I do expect those to recover quickly and have some decent gains again, but we'll see. More risk, more reward. 2019 better be good for the premium I'm paying.
I noticed awhile back that a lot of my funds were very Apple heavy, and so not as well diversified as I would have hoped (index funds included). They disclose this, mind you, but you have to read what you are buying. Anyways, I moved more money towards international and mid-caps to try and offset risk. Index funds have a way of being frustratingly constrained. It's not a silver bullet is all I'm saying.
Don't get me started on bond funds. Total, total crap the last few years. REITs same way.
The only really decently reliable returns I have gotten were from my own portfolio of stocks (not a fund) and some high-dividend yield funds. But even dividend paying stocks nosedived last quarter (Q4 2018), which I attribute directly to the FEDERAL RESERVE and its fuckery with the funds rate.
Everything is manipulated one way or another, never forget that. It's hard to be a small investor with others moving billions around all the time.
If you're still reading, I ditched a lot of bond funds in 2018 and went towards shorter term individually purchased bonds and even brokered CDs until interest rates settle back down.
Vanguard's bond funds are just kind of trash and don't do what they are purported to do for your portfolio which is try to solve the ever-elusive correlation problem. Many times, I've watched bond funds move in lockstep with equities because the Fed is king. Not a safe haven during a big drop, just smaller losses?
The people on Bogleheads will hate me for saying this stuff. If you're new to investing or naive or don't care, just do a 2-fund portfolio with total stock and total bond and call it a day. There.
RIP John.