First, all of the retail lists that I've seen lately (and package photos) have been absent Phineas and Agent P, which means they may be in Wave 3 after all.
Second, putting Ferb with a non-essential character, like Candace, is good business and exactly what they're doing by releasing Buzz and Jessie packaged together. It would absolutely make perfect sense for them to do it. I also think they know that Doof would sell well on his own (like Phineas and Perry).