Paul Madara was the first person to ever unlock the MS so besides his brother there probably where no others. Also the fact that using the MS has damaging side effects is probably why Madara doesn't spam it cause he knows it weakens him. It's reserve move only in the most desperate situation.
The fact their vision was getting worse from using wasn't a point lost on them hence why they where not able to spam it. You can only spam the EMS because there is no backlash pain and blurry vision from using it.
Madara not using Amatersu is for the same reason he doesnt spam Shinra tensei STLYE. Kishi likes each hcarter to have their own unique fighting style which is like their trade mark. Sasuke is the one who will be using Amaterasu heavily so he doesn't want Madara to steal his thunder in that regard. Its the same reason Sasuke doesn't use shadow clones because that's Naruto's style.
Keep in mind it was Obito telling the story not Madara so the so called facts where not first person but a hand me down story.
This chapter in fact makes more sense cause if Izuna was perfectly healthy why didn't he take Madara's eyes. It make sense that he was dying so he left Madara his eyes to protect the clan as both their vision was getting weaker.