Going for population centres and cities would make more sense than the 80% rumbling.
Thinking about it, to achieve Eren's goals and avoid common sense added problems, a rumbling that targeted population centres and cities would be better than 80%.
People are still not evacuating in time either way.
It avoids destroying entire forests and ecosystems. So lesser of an ecological collapse.
It probably kills more people but destroys less peoples so arguably less genocide.
It destroys civilization more completely so: capacity to war is further done away with; there's a larger diversity of people and we know a lot of times that correlates with less cooperation; building on that, capacity to remember is also done away with, the whole Titan stuff will turn into a morality tale like God flooding the world for a man becoming evil (YHWH, Zeus) or making too much noise (Enlil). Either way in all versions of the myth no ill will is placed on the gods so I do think there's high chances that also happens here and the titans specific cycle of hatred is gone.
And better yet for Eren gets to see even more of the book scenery. While probably feeling less guilty.