I like the lake, cause it makes sense for water to pool at the base of a fall, but it looks... off, somehow.
Without the lake, it looks a lot plainer than it did before (insane, because your falls are gorgeous!)
I went back to your original picture and I think you could pull off the quad falls if you wanted - the problem was the river splitting, right? So make it a second river?
(Better than mine, of course)
But, either way, if we go to the lake issue... it looks like the falls are hitting 2 different heights of land.
So when you make that into one big lake, it looks like it should be spilling over the side (or have a mini-falls in the lake) and the river would'nt form there.
Either way, the water isn't going to get narrower so suddenly under the falls... that's a lot of momentum behind the water, so it will move fast/heavy and cover/erode slightly higher ground at first Also, there are some areas (without the lake) that still look like they are on a hill. You might add a tiny amount of spray there? Or maybe it's my horrible water that makes it look that way?
All that being said... I think all the versions are lovely, and whichever you go with will be fine