It is undeniable that AY has a responsibility to offer rebooking as an option instead of a refund, whether BRU or DUS count for that purpose I do not know. AY has rebooked on other airlines previously, though they may be a bit resistant to it. Similarly, both Finnish and Dutch courts are completely useless for small claims (in Finland you'd escalate to a consumer protection authority first, but they do not have legal power and Finnair has ignored them in the past), so don't expect much..