Why shouldn't Gear 4th be Strong enough to defeat an Emperor?

##2.5 Years Ago - Gear 2nd

To put things into perspective, Luffy's best Gear was Gear 2nd pre-skip and it even carried on to be useful into the New World to defeat a lot of his enemies:

###Pre-skip

Ennies Lobby
Thriller Bark

###Post-skip

Fishman Island
Punk Hazard

 

So, for about 2.5 years, Gear 2nd (his best Gear) has sufficed to defeat a vast majority of all his opponents. Now, Luffy's best Gear is 4th. The idea that his best Gear won't or shouldn't suffice to defeat Emperors is somewhat illogical because it is like believing Gear 2nd wouldn't or shouldn't have been strong enough to defeat his opponents when it was his strongest power.

 

##Presently - Gear 4th

Luffy's only been in the New World for what? 2 weeks and only used Gear 4th twice, yet it appears as though many readers rationalise that Gear 4th shouldn't be able to even hurt the Emperors even though it's his strongest power? It's not like Luffy is going to have a Gear 5th when he's barely had the chance to showcase Gear 4th mano a mano.

Truth is we're likely going to rely more on Gear 4th for a good length of time before we see anything new if there's even a Gear 5th in the works.

If Gear 4th (his best Gear) cannot hurt an Emperor and he's supposed to defeat an Emperor to be Pirate King, then I think the readers have just convinced themselves themselves that nothing will absolutely under any circumstance be able to hurt an Emperor; Emperors are thought off too highly.

That would be akin to expecting Luffy with or without Gear 2nd to be unable to defeat any of his opponents pre-skip.

 

##Catch-22

The irony is people state or believe Luffy is too weak to hurt an Emperor, but believe he will one day defeat the Emperors without a Time-skip; the catch-22 here is if he suddenly gets a power-up, they'll complain it's a deus-ex-machina which no one wants and if it turns out Gear 4th is strong enough to tango with the Emperor, it's an ass-pull as it would be so eloquently put; even more perplexing, some seem to not expect a time-skip, but clearly express sentiments pertinent to the belief he simply can't take on Emperors or Admirals.

It makes the reader seem pretty unreasonable regarding Luffy's strength and what he should be able to do at this point with the exception of Awakening which isn't a random power-up, but one established.

 

##My Conclusion

Point being made is, it's only logical that Gear 4th should already be enough to fight the Emperors especially since there will be no time-skip and more so since no one has really put up a good fight against Gear 4th yet.

###My Question

Why shouldn't Luffy's currently best gear which he's only showcased for 2 weeks not suffice to defeat his current opponents?