Seriously: a plant takes around 8 weeks to bloom, and can stay in that state for another 8 weeks. That is plentiful time to harvest and not all at once. Also, while the first one is blooming you can grow number two.

As someone who growed stuff at home in the past, it makes perfect sense to me.

With 3 plants you have always one blooming and two following. Time it correctly and you have a constant flow of supply without ever having more then 50g of dryied products.

After you are done harvesting, dispose the rest of the plant and be fine. As the stem of cannabis is mostly water, it will not weight anything near 25 g if dryied. If it does, your plants are larger, and I think this may be intentional to limit the amount of products that can be harvested. Over all, while not perfect, the law is much better then many seem to want give credit for.

I was co author of the largest pro canabis petition ever in Germany, and the author of the anti-alcohol petition (reusing the arguments of the lawmakers why canabis can not be legalized, and just replaced alcohol with canabis). I am fighting for this since 20 years. And this is a huge step forward. Yes, it is limited. But the limit is imposed by the EU and not the German government.