I think efreet and djinn should be the same creature type. Historically efreet were considered to be a subcategory of djinn.

What is your guys' take on this?

I don't think the historical accuracy argument carries any weight. If you use that, ghouls would also be classified as djinn. Also, in traditional European folklore, "goblin", "elf", "fairy", and "spirit" could be used more or less interchangeably. Magic thus tends to follow established fantasy tropes more than it does the original source material. And there, it's common for there to be a distinction between fire-associated Efreet and air-associated Djinn/Genies. At least, that's the distinction modern Magic makes. In earlier Magic, the distinction was far less clear. If you'd suggested the merge back then, I'd have agreed.

I'm not sure about goblin and elf. But then, I'm mostly going by the books of Terry Pratchett.