Even the arguably strongest boxer in the series Takamura struggles against world class foes.

The only people Takamura struggles against are champions or when Morikawa decides to do a comic relief fight, and mostly because of his weight control.

Ippo struggles against nobodies.

Ippo isn't some genius who will suddenly start dodging all the opponent's punches and get a flawless victory.

I don't see why not. Not only he has the small stature and experience against some of the fastest fighters in the story needed to be able to dodge stuff, early Ippo was also capable of improvising against his opponents. Fighting in a southpaw stance in his first professional fight and predicting Saeki's moves in order to hit him are good examples of it. Hell, even a bona fide genius like Itagaki still can't beat Takamura's leaf challenge. Ippo isn't talentless in any way or shape.

He's going to struggle, this is Morikawa we're talking about

Which doesn't mean he will make Ippo being an underdog that can only win a fight after being an imitation of a sandbag before hitting 1 lucky punch (and he couldn't even do that anymore, since apparently all of his recent opponents can tank his punches like they were nothing).