The point isn't whether Zoro wasn't allowed to fight Doflamingo because he would have beat him (very debatable) nor his "even clash" with Fujitora ("even": Fujitora was fine, Zoro was damaged).
The point is that, in spite of these headcanons of yours, Oda never made the slightest effort to give Zoro an actual versus comparable in strength to Doflamingo or Fujitora. Why? Because, first of all, Zoro probably wasn't as strong as you may think in Dressrosa, and second, Zoro took the role Oda gave him without taking into consideration any "power level" clue some people here are obsessed with; hence why he wouldn't have made a big difference in Whole Cake: because the plot didn't necessarily require him to do so and he'd arguably end up just another member of the escape plot.
I mean, it's not a coincidence that he's getting to participate precisely now in a fight aganist the emperors: it isn't about him being stronger or weaker, it's about him being a member of the Worst Generation and Oda wanting to pull a "old versus new" with his plot. This situation is possibly not strength-driven and what Zoro gets out of this exceptional scenario, and what Oda consciously gives him on a regular basis, are lesser (and weaker) enemies than the main (and strongest) villains.