I say it's forced cause it doesn't make sense.
Coby started from a level weaker than kid Luffy, 10 year old Luffy! I can buy him becoming strong maybe like 10 years into the future in epilouge, but not at current timeline.
His persona also doesn't fit a conqueror's haki user at all, which would be a requirement if he has to become a DF-less top tier.
Coby is also a massive Luffy fanboy
Imagine Garp being Alvida's bitch slave and giga fanboying Roger. Pathetic.
Smoker on the other hand, was THE marine antagonist of Luffy for the entire pre timeskip. He was stronger than Luffy for the entirety of the pre TS, has displayed very high will power (first marine shown the actively go against the marine orders), and has the demeanor fitting of the series' marine antagonist.
His progression to being the leading figure of marine rebellion would've been very organic and natural narrative progression of the character.
That make no sense he has been training his ass off for 2 years plus with a top tier.
Getting stronger faster is a given, look at how fast all these other characters grow and he as the persona of hard worker which fit a conqueror haki user.
Law went from get unfair from don to fighting a yonko in 2 weeks .
Him being a luffy fan boy did not stop coby from trying to fight him at marineford where he awaken haki even before we see smoker use it at even younger age than luffy .
Plus as we can see you can be rivals and try kill each other and still be friendly etc etc as seen from Roger and Garp or WB and Roger .
Also smoker don't have the balls to be the marine rebellion leader , he did not even bother to call them out during marineford which coby did when he notice how blood hungry they were .
He him self said he could not ge the warlord system destroy like fuji did and here we are once again having coby show back bone giving up him self for all those marines .
Still at the end of the day smoker could have never been luffy main marine antagonist and neither will be coby when
Akainu there and luffy might not even fight him since Imu there for the WG .
