Sinking Maw resembles the also-5th-level spell maelstrom in some ways, and differs in others. The swirling liquefied ground doesn't deal damage over time, but can be much more confining and harder to escape from than swirling water. If you really want to completely smother your foes beneath the earth and you don't mind hitting only one target, Living Burial at 7th-level is what you're looking for.

These spells do explicitly nonmagical physical damage, which leaves almost as many creatures resistant or immune to them as for fire damage, with fewer vulnerabilities. And that doesn't count temporary spells and effects such as stoneskin or gaseous form. This, combined with their other limitations in terms of needing suitable earth, affords them a bit of extra potential power in other situations.