A flat market is in many ways the best place for actively managed long-short funds to differentiate themselves. Given where overall market valuations are we are probably past the point of double digit market gains for a while (although I could have said that years ago). So I think that skillful active managers will be better positioned. That said, I recognize that I am an active manager so 1. I may be talking my own biases but 2. I think I can differentiate real investment skill from charlatans, which is very hard for even very smart non-professional investors
When the market churns flat I tend to outperform because I have a sizable yield component and my individual name alpha shows its strength. When the market crashed in 2008 I ended up the year on short positions so that really impacts longer run outperformance. In December I went on a shopping spree after being defensively positioned into it which left me much better off than if I had passively been long the whole time.
My point is that no one strategy fits all investing risk thresholds or environments. I like to aim for a nice 7-12%/yr with minimal drawdown volatility and hedges against nasty things happening. I look "stupid" if the market is up 20% in a given year and I am not. Over the longer term nasty things seem to happen every X years which has vindicated the approach thus far.
Generally, when I feel a region is looking good, I get into a mix of index and broad actively managed (with a liking for smaller companies). Reasoning... not much beyond thus far it seems to have worked out well. Those active funds have certainly outstripped the indicies, but with such a small sample size, I'm not so much datum as noise.
I wonder if there's a middle-place to be found between plain dull index, and mad-as-a-hatter active managed.
I believe 401k's commonly limit themselves to a group of funds and there is sometimes no "index" option, so I would imagine there are people who are in actively managed funds here.
On that same score, I find rolling one's funds into an IRA whenever possible (change of companies, acquisition of your employer) to be very helpful!
Having direct control of your assets is generally a good thing. One advantage to rolling your assets from a prior employer's 401k (or your own IRA) to your next employer's 401k is that it allows you to fund a backdoor Roth IRA with the single year's contributions. Otherwise you'd have to convert your entire IRA which could be a large (present day) tax bill.