Terra is far from awful. I've not used Luna enough to judge whether it's significantly better than Luna, but at least via GitHub Copilot, Terra is leaps ahead of Sonnet 5.
Luna is not bad, but... you feel is a small model. It have less knowledge. It's ok for purely agentic stuff (web searching etc).
It's not awful, but if you are doing research or anything complex and don't want to spend hours fighting it, Sol is not an option.