“So, Rav Akiva Eger held that smoking is good for your health. How ,then, can more recent poskim hold that it’s assur? ”
Asides that the very comparison is A”H (as pointed out by DY). The very issue about smoking on its own is really misquoted and can still be relevant.
For starters you got the wrong Achron, it is the Pnei Yehoshua NOT Rav Akiva Eiger. (at least look up your sources before making a bold statement)
He states it in regards permitting it on YT, as it has to be Shava le’Chol Nefesh to consider as Ochel Nefesh, and many people do not smoke etc. so he simply says being that it helps for digestive reasons it is permitted.
He is simply saying it based on how it was accepted at the time and how it was utilized. And BTW one can still make that very argument nowadays.