Ahem. What are the benefits of entangling the enemy? Lowered AC and hit roll. As has been said, not exactly helpless (unable to act at all) as might be the result of many other spells (Color Spray, Sleep, Tasha's Hideous Laughter, etc).
Another issue many people seem to be forgetting here is that while it forces the enemy to rely on ranged weapons...it also forces other party members to do the exact same thing (unless you are able to place the center so as to put the enemies on a boundry...but it becomes much more easily escapable then). So, ON TOP of the circumstantial nature of the combat terrain, it relies upon the party having certain capabilities to use effectively.
DC:20 is indeed a high ability check. However, it's an ability check to allow someone to circumvent the spell AFTER failing the save DC.