Although if we're being consistent, the Northmen should have been completely decimated as well, and there were far fewer of them when the battle began. I mean, the North was basically wiped out three times - at the Twins by the Frey/Karstark/Bolton betrayal, at the Battle of the Bastards, and then at the Battle of Winterfell. And yet...there are "thousands" of them waiting to carve up the Unsullied and Dothraki.
They could have done it if the forces attacking KL had included troops from both the Vale and Riverrun that hadn't been at the Battle of Winterfell...but it didn't.
ETA: That's what's so frustrating about a lot of these nits. There were ways around all of them what wouldn't have taken much effort or screentime. A 30 second conversation in which Danaerys explains why she is leaving some Dothraki and Unsullied behind to hold Dragonstone, for example. There's the troops she needs to make the numbers work.
When Jon kills Danaerys, and the Unsullied rush in...Drogon backs up Jon. And that's why the Unsullied and Dothraki get back on their boats and go home. Cool scene, no arguments.
Lots of little things they could have done to make it look like they actually cared.