The most enjoyable healing is found in progress and blind fights. The issue with levelling is that the content has been ran hundreds of times so people aren't making mistakes. You can rather specifically look for newer players to play with or you can progress Dawntrail content like Extremes, Savage and such in parties that are progressing it. That's kind of the case for most games, the most engagement for healers is when people are learning things and making mistakes. Once things are optimized, it gets more boring.

I'm not saying this is the way it should be, I'm just treating your question in good faith and telling you my experience in finding healing that is enjoyable.