In 2014, markets were doing well and I didn't look, but I bet if I did, I would have found an article saying the same thing, 'don't lump sum now.' But based on the statistics, I went ahead and did it, to the tune of $120K. I had been saving cash for about 11 years and just sitting on it in "High" yield savings accounts and CDs. It was meant to be for an eventual house purchase. To this day we still rent, and I'm glad I invested when I did. My only regret is not having done it sooner.
IDK where you are in your FIRE journey, but if retirement isn't right around the corner, I say throw it in. Someone else here once said "the market is always at an all time high." Obviously that is not true and we have had dips, but generally speaking, it does tends to go in one direction.
DH and I are currently socking away over $5K a month, plus we lump sum $11K every January on top of that. Our rule for investing is always sooner than later. You may be right that you'd be better off DCAing in, but you might not. Either way, just set a standard and go with it, that way you don't need to think too hard. Yes, that's right, my investment strategy might center around not having to think too hard... Good luck and be glad you are in a position to invest such a sum!