As observed in S8E4, Daenerys needs all the people she can get to fight Cersei. Why didn't she ask Dario Naharis and second sons to join the war?
They are on the other side of the world. Reaching them with the message and then waiting for them to sail to Westeros is not something Daenerys would be willing to wait for. Remember that she refused to give her troops even a few days rest after the Battle for Winterfell before marching on King's Landing.
Her (dubious) reasoning for this was that her army would be getting weaker, while Cersei's grows stronger by the day.
Dany was insulted and looked ready to start burning people when it was suggested that they try to rest from the battle of Winterfell.
When Tyrion and others arrive at the camp outside King's Landing on the night before battle he tells Jon and the others that Dany wants the attack to begin "immediately." Glances were exchanged and Jon said they would attack the following morning. It won't surprise me if Dany brings up that delay in ep 6 next week.
With that level of urgency from Dany, there is simply no way that she was going to sit around waiting to see if the Second Sons could make it across the sea from Essos without being sunk by Euron's fleet.
And beyond the issues of time and logistics, if Dany wanted to keep having sex with Daario then she would have brought him with her in the first place. She left him behind because he was not suitable as a queen's consort and nothing about that has changed. Daario is probably the last person she would call to her side.
Don't forget he was essentially appointed as the head of law enforcement on her departure. She tasked him with keeping the peace and keeping Mereen from reverting to slavery or just generally crumbling into chaos. Removing him would basically mean accepting that Mereen may crumble and her changes undone.
Also, they probably couldn't fit his abs into the budget.