I think his point is that they did a poor job of depicting how many survivors there were after the battle at winterfell. They showed all the Dothraki charge the undead and very few return. Now, it could be that they intended for many more of the Dothraki to survive that charge, but they didn't do a good job of communicating that to the viewers. The same is true of the Unsullied, by the end of that episode you got the sense that the armies were almost completely wiped out, they completely lost the walls and there were no scenes of thousands or even hundreds of men waiting in retreat.I’m not defending the writing, I’m discussing your critique.
If you think they attacked kings landing with fewer than 100 survivors we are watching a different tv show.
Did you assume that the funeral scene showed all the survivors? That might be your mistake.
There were ~100,000 Dothraki That dwindled down to a few hundred in the Dany speech.
There were ~8000 unsullied down to be maybe a thousand.
Cut to a few episodes later and there they all are! Enough to man a fleet of warships and an army to march south.
My first suspicion was that the reason for this was that the episodes were directed by different people, but Miguel Sapochnik directed them both. So there's really no excuse for it.