I've been thinking about how ridiculous the Yunkish soldiers are and then it hit me: Yunkai and Astapor haven't been to war in centuries.
It's been a while since I've read ADWD part 2 but I know that the army had a rotating roster of enslavers and they all had a gimmick. Some kept their soldiers chained together, one guy had soldiers on stilts, and one had half-naked soldiers with erotic shields. It's a ridiculous pageant that would quickly fall apart when faced with real combat. I kept wondering if the Yunkai'i and Astapori were that stupid until it hit me that they've been letting the Unsullied do most of their fighting for the past few centuries and probably use enslaved Unsullied generals who went with Dany. Yes, they have a few thousand enslaved soldiers defending their walls but I don't think they've been on the offensive since Valyria conquered them. They have no real experience with how combatants should dress or be equipped and since they're entitled slavers, they're not gonna stoop to asking one of their enslaved soldiers if they're waging war correctly. The sellsword companies they hired to fight for them must be annoyed as hell cuz they're professional killers being dictated to by squabbling rich idiots who are dressing their enslaved soldiers in the Essos equivalent of clown costumes. Which brings me to how I think Barristan Selmy will win the battle outside of Meereen. The slavers' army is a mix of mercenaries and gimmicky slave soldiers that are definitely going to trip up the sellswords, assuming they don't say "Screw it" and start cleaving their way through their own allies so they can fight without fools underfoot. Predictably, the Wise Masters will bemoan their "destroyed property" and demand reparations but the sellswords will all switch to Dany's side once she returns cuz their current employers are fucking ridiculous.