What you saying is exactly why its bad. Changin g decks over and over with every different team you met is not convenient. Deck system is fine for those people who can set 3 decks or less and swap between them with no need to change anything in them. It usually happen for DD classes or when you play always with the same team (read: with your own sidekicks/heroe's or always with the same guildmates/friends). It is horrible if those 3 decks is not enough and you have to get through all passives/spells to review them if there's something you can replace or not. An example could be if i join some random team who goes enurado, and then i have to ask myself if i should bring my revival spell that i normally dont have in any deck or not for example. That again makes me in need to throw out some useful spell from x deck, and then i also need to use my future sight abilities to know if i will be in need to use dolls or not, and based on that i will have to choose different deck, wich i also need to modify for revival spell, and i also need to consider whether we will need my heals or not, should i let these low levels do their best and just do my own stuff withotu carrying of their safety or should i try to keep them all alive, rush it recklessly or play it safe but longer. Each decision, with every different team is important, but that just makes it a horrible experience in longer run. Maybe if fights were more significant, if spells were more universal and less restricted, maybe if there were more decks available with possibiity to name them without going to notebook, maybe if i could have all spells maxed earlier then at 200 lvl to actually juggle between spells effectively without worrying that i won't have dmg dealing spell.... MAYBE then it would be acceptable somehow. Right now the best you can do is to stick to 1 deck and play with it all the time. For me this is very limiting on classes wich used to be able to adopt to unexpected situations in combat.
And this is why wakfu is dying for me. I don't know why you even want to argue about my own personal feeling.