So, before I start: I would not have said anything if you hadn't gone all "uhm actually" in a condescending tone towards someone who's just doing a silly little twist on the taxonomy thing on some inconsequential thread on the internet.

Might I point your professional attention as "scientist who studies lions" to the fact that the thread is about how "Panther" is not a real species but one of two other species with a different level of melanines in their fur? Good.
Now, would you care - in your scientific scientist way - to shift your attention to this thing you said:

They’re both. A panther is a panther and a member of the panthera genus.

My layman brain does the big confoosy-boosy! Isn't the point of the whole "useless party knowledge" type post here that panthers are, in fact, not panthers because "panthers" are not a species at all?

You said a lion is a panther,

They said that because - and this is true - "panthera" and "panther" are the same word. "Panther" is ancient Greek while "Panthera" is Latin and -depending on how your language adopted the terms- the plural of "panther". So an animal that belongs to the "Panthera" genus does belong to the "panther" genus, depending on the host language used. Since we already clarified that "panthers" are not a species at all, the only "panthers" are the members of the panthera genus. So yes, a lion is a panther. So is - to further ridicule your "sciency scientist"-attitude Panthera uncia. So yes, we have thrown the snow leopard in there, too.