I think the key here is that Simba is not a "fakie" company as we would normally think of a Chinese factory making and selling random lines replicating existing brands. Simba are a very big and very well established company in Germany, as such they have more of a significance to Hasbro than other random manufacturers.
As plenty of German members here will tell you, many toy stores carry more Simba pony inspired products than they do Hasbro. Its probably just that Hasbro are feeling a little squeezed out of the German/Dutch market - combined these countries probably offer the first or second largest market for Hasbro in Europe. So loosing out is not something which is going to sit well with them.
So its not just that they can go after a European based company, its that in this case they feel its in their commercial interests to put Simba on the back foot with any pony styled toy line.
And to note its not just China that Hasbro would struggle with this in. Plenty of other countries do not recognise the copyright of toy lines. In fact in the UK, current precedence and laws do not protect copyright on a toy line. I wonder if perhaps a similar precedence exists in Germany and hence why the case was raised in the Netherlands rather than Germany?
Also there is no patent on the product any more so they are prosecuting on copyright; that means the pony does not have to "look" the same but has to be a replication of the concept. And this is a replication of the product - fantasy pony, brushable hair, "symbol" on hip. Clearly in Dutch law this is enough.