As the title is saying, considering that the Costume Chamber is on only every two months and we have about 20 S1 5* heroes, I would see it that they should increase the number of featured heroes to 3 or 4 for each round. Otherwise, basically it takes more than 1.5 years to cycle through all heroes.
Having each 5* costume featured every year at least would be desirable.
Hm you make a good argument about it taking so long to go through the rotation, but as someone that desires maybe five of the costumes and would be okay without the rest I’d have better odds if it was a singular featured hero. I doubt two or my desired heroes will be featured at once. So having a singular featured hero would increase my odds for that one hero.
But I think your logic is more rational so I’d be quite okay if it was increased.