The typically fan overreaction imo "The Phoenix" which has been in some terrible X-men stories can't be used now in some terrible Avenger stories? Apocalypse and Phoenix might be two of the most overrated concepts in X-men lore. Nothing has touch the heights of the Dark Phoenix saga and I would be with people on this if the Phoenix was being used in these all time classic stories but no most phoenix stories since has been bad or average. The best thing to happen to Phoenix is that has been removed from the X-men franchise and writers can't try to write their bad phoenix stories as X-men stories.
As for Echo it is nice that Native American and disabled character is getting some spotlight. The only downside for Echo is that Phoenix powers always go away at some point and if this status with her becomes popular her regular powerset doesn't even come close. But other than that Marvel has made this character the one of the highest profile in the Avengers book with this move. Also Echo is in the Hawkeye Disney plus show and She is getting her own spin off show. So for the people who are thinking this a flash in the pan move they are big things going on for the character.