Two monoprotic acids vs. one diprotic acid
Your intuition is right, because a potentiometric sensor (a $\mathrm{pH}$ probe in your case) does not know the source of hydrogren ions, it only senses the presence of hydrogen ions. The same is true for any other detection mode. All we care is $\ce{H+ + OH- -&gt; H2O}$.

It can come from two monoprotic acids or it can come from a diprotic acid. In order to make your wish true, $\mathrm{p}K_\mathrm{a}$ must be less than $\mathrm{p}K_\mathrm{b}$. They cannot vary randomly and they cannot be equal.

However intuition is not enough to prove a point. You have to pick numbers and simulate. Here is useful online tool to calculate titration curve and see how well they match.

pH Titration Curve Generator

Choose to add $\ce{HA}$ or $\ce{H2A}$ and $\ce{NaOH}$ as a base.