Idk why we think any matchup in any arc ends up being as clean as we think. Do I think Sakazuki, Issho and Aramaki wil be fought by the M3? Absolutely. Do I think Akainu has select Marines that were also conscripted by him to be his elite? Yes. But we've seen time and time again how matchups in this story never pan out or never end up clean at all. They have not literally since Alabasta.
Egghead and Elbaph are just the latest in showing us how this operates. Oda doesnt have the time nor the luxury to draw out 1v1 fights for everyone, nor does he seem to have interest to. He brought like 10 fightable Marines only have Kizaru do nothing and Zoro fight Lucci out of all people. Then he proceeded to bring 4 GKs to Elbaph and then removed one. We'll see if the paradigm shifts in a few chapters but right now its looking very similar as the last arc.
If its not clear already, he's saving an indescribable amount of enemies for the endgame of this manga, to probably not receive their time of say onscreen or to the level of detail people want from their fights. And that should worry or scare you because he refuses to remove enemies from the story.