I didn't find any good arguements you gave. Which one?
Ok, even if I change the word 'despised' and use the word 'teased', that doesn't change the Iris was a kid herself and so her catchphrase felt kinda annoying and hypocritical, and I don't think that I'm the only one who thinks that way.
And every travelling companions of Ash cared for him. That's natural. But Serena did care for Ash some extra bit. Whenever Ash is having trouble during a battle or so(like in the first Gym battle with Wulfric), Serena looks a bit extra concerned, and she also believes in Ash an extra bit. When Wulfric Mega Evolves his Abomasnow(during the rematch), doesn't Serena say, 'It's OK, Ash can handle this', or in the Ash vs Sawyer battle in the rematch, when Ash-Greninja was busy dodging the Frenzy Plants from Mega Sceptile, didn't Serena say, 'Don't worry, Ash is one with Greninja right now, they won't give up until they have given it their all, or during Ash-Greninja vs Mega Charizard X in the finals, didn't Serena say, 'It OK, Ash will definitely win''. See, she always showed some extra belief and concern for Ash compared to the other Pokegirls. This just shows her love for Ash clearly. So no, Serena isn't a May with plot-armour like you said.