There's another rather significant issue with getting logograms, which is that at max level, there are no sprites that drop mitigative logograms.

There are multiple sources of them prior to that, but only inimical logograms drop from 50-55 sprites post-adaptation, which seems like a pretty big oversight.

The only way you can get them in large quantities at 50 is by level syncing using a NM then killing whatever appropriate sprites can be found in their vicinity.