I haven't used PlantNet though I've been working on learning plant identification/taxonomy and have been using iNaturalist. Their models are limited by inputs, if you've got a wild angiosperm that's flowering it's pretty good. With human cultivars, even with flowers it's not always great, though no shade there, that's what I'd expect for visually trained models that focus on plants in the wild. If you aim it at a leaf there's not enough visual data to categorize, if you aim it at a full plant it's so-so. I mostly stick to flowering plants and have an easy time.