I'm not going to argue that with you because we have no idea just what Andraste precisely wanted. But, the Imperial Chantry refuses to divine aspects of Andraste thereby making them, arguably, part of the faith of the Maker but not Andrastianism itself.
But it can be argued, because we have official sources. This is what World of Thedas says in page 123: "Hessarian declared the Maker the one true god, and Andrastianism the religion of the Imperium". In fact, it's one of the few mentions of the term "Andrastianism" in official lore, so yes, they are Andrastian.
The lore, including WoT, prefers the term "Chantry" to talk about this religion. But does that term require accepting the divine aspects of Andraste? Let's check the four core principles of the Chantry, according to WoT: "III. Andraste was the bride of the Maker, a prophet and martyr whose ultimate sacrifice must be remembered and honored".
It doesn't say that she couldn't be a mage, or that she has to be worhipped, just "remembered and honroed", something that the Imperial Chantry does. Saying otherwise is a case of the No True Scotsman fallacy, and very similar to real religious discussions; for example, the nature of Christ that was debated by early Christians. Most Christians now follow the Chalcedonian definition, but there are others: Arians, Nestorians, Miaphysites, etc.