Exactly. Acnologia has greater physical strength as a dragon than as a human, despite having equal amounts of MP. Igneel has physical strength pretty much on par with Acnologia. Natsu is literally gaining aspects of a dragon when he uses dragon force, and the dragon he takes after is Igneel. Why would he not inherit Igneel's physical strength if he's physically becoming more like Igneel?
If you want to say the Spriggans are country level based on hype, then you might as well take Mercphobia's hype of being on Acnologia's level at face value. That would make him stronger than all the Spriggans, plus Zeref. Anyways, none of the Spriggans can casually flood a city because their power was too great to contain. Stuff like Sand World is already a high-level move for them. Mercphobia wasn't even fighting seriously when he lifted the ocean.
I'm actually not too terribly concerned with how DF Natsu stacks up against Irene, or whatever it is you're trying to argue with Mercphobia here. The bottom line here is that Ignia with just one attack is able to make Natsu strong enough to defeat Mercphobia. Natsu wiped out all of Mercphobia's magic power for the foreseeable future, and would have kept going if Lucy hadn't stopped him. Unless Irene is much stronger than Mercphobia, and would beat Natsu with Ignia's flames where Mercphobia failed, then Ignia himself would oneshot Irene with the attack he used to feed Natsu.
@Verter said what he said. If he meant something else, he should have said something else.