The problems with our most loved-to-death U.S. national parks are nothing new. Overcrowding has been a problem for years now and solutions are constantly under discussion. If any of you park lovers out there are familiar with the "National Parks Traveler" website (https://www.nationalparkstraveler.org) you've seen some of the many articles/discussions on the topic, such as these:
https://www.nationalparkstraveler.org/2018/01/arches-people-proposes-solution-arches-national-parks-congestion-woes
https://www.nationalparkstraveler.org/2017/08/crowding-issues-national-parks-drawing-concern-and-brainstorming
https://www.nationalparkstraveler.org/2017/07/op-ed-yosemite-so-crowded-you-cant-park-youll-still-pay-enter
https://www.nationalparkstraveler.org/2017/07/acadia-national-park-officials-debating-how-deal-crowds
https://www.nationalparkstraveler.org/2017/08/yellowstone-visitors-say-park-too-crowded-and-congested-not-enough-rangers
Without getting into which proposed solutions I personally think are good, bad or simply unrealistic, we've managed to do parts of some of the most crowded on the lists - Arches, Zion, the Grand Canyon South Rim, Acadia, Bryce - multiple times in relative solitude. What does that take? Timing and footwork...and therein lies some of the issue. While I understand that not everyone is physically equipped to lace up a pair of boots, I think there are more folks able to do that than are willing to. Easy accessibility is great for non-hikers but it also encourages/adds to one-viewpoint-to-the-next road/shuttle/tour bus congestion. With minimal equipment, it isn't difficult for someone in reasonably good shape to explore some really nice, less-visited corners.
Skipping the summer season and rolling out of bed at dawn has been a good crowd-avoidance strategy but again, fewer rather than more folks seem to be willing to do that, and summer is often the only time families with kids can travel.
Instead of Zion, go to Capitol Reef. Skip over Arches and explore
Canyonlands.
Using the early-in, non-summer, less-visited trail strategy, we've hiked Devil's Garden and Tower Arch at Arches almost completely alone. Also climbed up to Delicate with the mob for sunset but waited until they were gone and hiked down all alone under a full moon. Religious experience, that! :O)
Capitol Reef is great; some really excellent hiking there, and we've had a couple of trails all to ourselves. Even the easiest, more visited ones are never really overrun, Hickman Bridge excluded, maybe.
Canyonlands; my favorite! We've done 3 units (Island in the Sky, Horseshoe Canyon and Needles), 2 of them more than once, and Needles, hands down, is Top 10 hiking with killer scenery and LOTS of solitude. My #2 in the Moab area is Fisher Towers; also ranks right up there on the "Best Hikes Ever" scale.
We've (sadly) avoided Yellowstone and Yosemite so far. I don't know if there's any good way to avoid the road mess in either of them. :O(