In 2017 we hit up multiple national parks on long trip in the early summer and were able to avoid big crowds for at least parts of the day by doing some more remote/difficult hikes and leaving very early. This was at RMNP, Canyonlands, Zion, Yosemite, Sequoia and a couple others. At RMNP just after memorial day we did one hike to some lakes and did not see anyone for 4+ miles. Only a small amount of snow near the end of the trail.
National parks are not where you want to go if you want wild/remote places. There are 10s of millions of acres of national forests, designated wilderness areas, roadless areas, etc that have rivers, creeks, lakes, mountain peaks, waterfalls, etc. Fairly common for us to go on hikes and not see another person. Just have to avoid the spots that get instafamous, like parts of the Cascades that are getting trashed. BLM land can have some cool spots as well. They are not as "stunning" as some of the national parks, but not being over-developed makes it much better for me.