Till today, I really don't understand the Alicia/Rose thing. Easily one of the more bizarre gaming controversies I've encountered.
On one end- I think the treatment of the characters themselves are fine. I like Alicia, and I like Rose. Rose winds up actually a WAY more interesting character than Alicia ever was, IMO. (which flies in the face of all the people pissed about Alicia's "absence" and subsequent hate for Rose as a "replacement") But all those biases aside Alicia has an interesting and valid reason that works within the games plot to need to leave the party early, but is still featured enough to make an impression, and makes later appearances in game. Obviously, all was done from a creative standpoint to tell the story they wanted to with the characters. Zesteria isn't the first JRPG to have a party member leave early due to plot reasons. Namco clearing wasn't trying to troll anyone, and just wanted to tell the story they set out to tell. But it obviously all blew up in their face. Then that DLC was made to try and appease people and that didn't go over well either.
But I guess it was the messaging that went wrong. All early previews showed Sorey & Alicia as the introductory characters- therefore to a lot of people- SHE was lead girl/heroine/waifu. I guess people really took to this particular "lady knight" character and really looked forward to adventuring with her. And then when it turned out she wasn't the lead, then came the rage.
How could it have gone better? Show Rose from the start, not Alicia? Don't show any characters early, Keep the plot closer to the vest, so people don't foster certain expectations, I don't know?. But definitely expectations got out of hand, and granted, Namco didn't bother correcting people on this perception - however I don't even know if they should have done that since it would have spoiled things with the plot, but then again it didn't go over well, so I don't really know what the right answer was.
All that said, I won't deny the game has its problems, major ones, but for me the least of them was the Alicia/Rose thing. But alas it was a big deal for many, so... yeah.