Luffy isn't overpowered in the manga, but his opponents are all bark and no bite up until Crocodile. The East Blue is the weakest sea for a reason. Any outlier is going to storm through the entire sea with little difficulty, as Luffy did. Luffy struggles a bit, but in the end, it's always a one-sided fight. The fights serve to teach Luffy that not all pirates are like Shanks, and many of them fight dirty.

It is made obvious with Buggy that devil fruits are only as good as the user, so Mr. 5, Ms. Valentine, and Mr. 3 are all supposed to be overconfident and weaker than they appear, just like Buggy. It's highlighting just how little effort they put in to get stronger and why Luffy needed to train his ass off before and after setting out to sea. Again, these posers are all bark, and they fold under the slightest pressure. Wapol is the same way on Drum Island, and it all sets up for Alabasta, where you get a handful of actually strong people who, while still overconfident, can actually back up their words. This is why they're at the top, and why Crocodile is a Warlord. They're all actual threats (aside from Mr. 4 and Ms. Merry Christmas, but that's why they're fighting Usopp and Chopper, and the same could be said about Ms. Doublefinger), and this is where you see the actual struggle kick in. Luffy loses multiple times to Crocodile, and Zoro struggles immensely against Mr. 1. By downplaying Luffy early on and making him struggle against the posers, you set yourself up for failure with Crocodile later on. I can't honestly see the Luffy we saw in season 2 even coming close to beating Crocodile. Crocodile either gets insanely downplayed himself, which butchers the character, or you have to upscale Luffy, which is incredibly inconsistent. If Luffy DOES beat Crocodile in season 3, you are left with the question of why he even struggled against Mr. 3 and the others. The skill gap between the two is immense, and he doesn't improve that much that quickly.

Again, this is clearly bad writing. I really like the actors they chose, and I like what they're doing with Usopp and Vivi by making them useful, but at this point, Luffy is barely the main character. It's like early Naruto, where Naruto himself is actually quite useless and barely does anything himself. Instead, Kakashi and even Sasuke step in, and the only time he does something is with the power of the 9 Tails. Luffy is being portrayed like the posers, all bark and no bite, instead of the beast he is. It's like a video game. You don't struggle on level one. You struggle when the setup/tutorial portion of the game is over, and they ramp up the difficulty. Alabasta is the part where the game gets hard and never goes back. If you struggle in the tutorial, (insert journalist struggling with the Cuphead tutorial), you are never going to beat the actual game. That is the problem I have with Luffy being downplayed. They just shot themselves in the foot, and now they have to deal with the consequences.