Your thoughts are correct on this. Therefore, both sentences are correct (“Lions are dangerous animals” would also be correct. This would refer to “lions” as a general topic.)
Sorry, but I disagree with the whole argument. When speaking of the species in general as the topic (raion wa [Jp]), all three sentences carry the same meaning and no more:
A lion is a dangerous animal.
The lion is a dangerous animal.
Lions are dangerous animals.
They are simply alternative phrasings. There has been a lot of misinformation given out at this site recently, but if you all wish to continue advising each other on the English language, I for one do not have the time or patience to constantly oversee and correct.