Waterfalls in Washington are some of the best!!
Yeah, really the only way to get good waterfalls when bright sunlight is on the water is to use an ND filter. I use a 3-stop ND filter; it cuts the light by 3 stops. You can get darker than this, like 6-stop or even 9-stop (or not as dark, like 1-stop or 2-stop) but 3-stop has worked well for me all around.
In my opinion, the editing appears a little over-done. The dynamic range was just too great, but perhaps learning how to use Luminosity Masks could help make a more natural looking blend: https://digital-photography-school.com/exposure-blending-using-luminosity-masks-tutorial/ Jimmy MacIntyre has a lot of great tutorials on how to take care of high contrast scenes like this.