I think that as long as you go the opposite direction of what's typically intended for a class that you're going to have a high chance of failing. Have you considered going with a Druid, and going the complete opposite direction of their subclass? A Circle of the Land Druid trying their best to focus on Wild Shape could be funny. From a roleplay perspective, I think it'd be great if it were one of those situations where their parents pressured them into that direction, like a family full of doctors expecting you to be a doctor. So you go to college and actually work through your degrees and successfully complete them, but your true passion is, I don't know, let's say cooking. In this case, the Druid comes from a long line of Land spellcasters, but he's always envied the Moon primalists and has a lot of conflict and turmoil trying to embrace that, but is relatively ineffective.
Thanks, Tzelanit. This is a lovely idea. It will be fun for the role-play to try and establish what happened in life to have them as they are.
I will have to investigate the possibility of Cirlce of the Land Druid trying to be a Wild Shaper, but a) which other character would they replace? and b) wouldn't a Druid be too useful in the Party?