My experiences mirror many mentioned here.  I'm now using S&P500 Index Funds for nearly all of most stock holdings.  I used to try to juggle many funds in many accounts across various sectors trying to beat the market averages, but I usually ended up with about an equal number of hits vs misses.  Ultimately I came to the conclusion that it wasn't worth the effort.  Much simpler just to consolidate all the stock holdings into S&P500 funds with low fees (like Vanguard's). 

That's about 60% of my portfolio.  The other 40% I've poured into LC, Prosper, and Peer Street, with the intent of that being a less volatile hedge to the stock market.  While the hedge strategy itself remains solid, the returns at LC have not.  I started liquidating my non-IRA LC account in January, rolling those proceeds to Peer Street.  But it will take 3 years to complete. 

I still have a big chunk in a LC IRA ($260k) that's doing poorly.  The 3-year timeline to liquidate notes combined with the many-months process to transfer IRA funds makes it really hard to cut and run.  I turn 59 1/2 next May though so I may just start routine withdrawals instead to convert funds to non-IRA where they're easier to move around, for part of it anyway (depending on my tax situation each year).

My Prosper account seems to be holding up with reasonable returns though (~6-7%).  Same with Peer Street. 

LC has turned out to be a major disappointment.  I've still made money overall but the returns have been so poor that I'm well short of what alternate investments would have produced.  Ironically, I liked LC much better than PR initially.  Now it's PR that I'm happy with (relatively) and LC that sucks.

I stopped reinvesting at the start of the year and started withdrawing all cash every few weeks from my 3 year old account that I'd grown to $274k. 

My June statement shows a monthly loss of $457 (-2.0% annualized rate). 
YTD I'm squeaking out a measly $1089 profit (+0.8% annualized rate). 
For 2016 I showed a +4.6% profit.
For 2015 I showed a +8.7% profit. 

That's in my after-tax LC account.  It's easier to phase that one out by simply xfering money every few weeks.  I also have an IRA account with LC with substantial money in it as well ($234k).  Got another year before I hit age 59 1/2 where it will be easier to start withdrawals from it, so I'll just keep it going and reinvesting.  It's too much trouble to processes rollover transfers from it over and over as proceeds roll in.

Fortunately, that account is doing better... 
June profit is $1600 (+8.2% annualized).
2017 YTD profit is $5340 (+4.5% annualized).
For 2016 I showed a +5.7% profit.
For 2015 I showed a +7.5% profit.

The only real difference in the 2 accounts is that I started the IRA in 2015 and the regular account a year earlier in 2014, so I have more "aged" notes in the regular account that's doing terrible.  All my notes are 36mo, so my regular account has already cycled fully through some of the notes by now.

I'm having much better luck with Propser than LC.  While my real LC returns keep dwindling way down (4.6% in one acct and 2.8% in the other), my real Prosper returns are holding up fairly well around 7-8%.  Not great but good enough to keep me happy as a more consistent return and a hedge against the high volatility of the stock market.  I keep about half of my total portfolio in S&P500 funds and the other half in peer-to-peer lending (LC, Prosper, and Peer Street).

That's using a basic auto invest filter (not API).  My account page shows a 6.72% Seasoned return, 7.22% All-notes return.  The account is 3.5 years old.  I only buy 36mo notes.  I have ~1900 active notes, mostly B and C grade but some D/E/HR too.  It's a little tricky to calculate a "real" return (true account value over time) longer term since I've been adding funds to my P account as I'm draining my disappointing LC accounts.  But I do have two clean periods for comparison where no funds were added.  One is the last 4 months, where my account value increased 8.2% (annualized).  The other was a 9-mo period in 2016 (Apr-Dec) where I also experienced a real 8.2% annualized return.  I added funds early in 1Q2016 and 1Q2017 which took a few months to invest into notes so I don't have clean data points for those months.

I think I'm done adding more money, and I don't plan to withdrawal any for years, so I should be able to better track long-term returns from here on out.  If I can keep getting around 8% real return, I'll be happy.