Depends. Without good durability and hardening (both of which Ifrit Jambe depended on), it is basically Diable Jambe. Which, I guess should still be at the lower end of the high tier spectrum. On the other hand, other abilities depend on Haki too; be it Katakuri's Mochi or even Luffy's Nika fruit, where he mixes CoA and CoC with it. Bajrang Gun is pumped full with Koka, Barrier, internal destruction and Haoshoku.
Best case scenario: Super durable body with maxed out Hakis. I'd say as much as low top tier. Using super hard Koka, Sanji could make his leg even hotter, possibly inventing Surtur Jambe. Then add internal destruction Haki and high level of Haoshoku coating, and you will have a synergetic effect with enormous attack potency and speed. You don't really need large AoE, since AoE won't directly damage the opponent. Instead, you focus all of your potency towards your opponent.