Every confirmed Digivolution line is canon, whether or not it appeared in Adventure. Which one you prefer is moot - Ophanimon is a canon digivolution. Her inclusion in Frontier as opposed to Magnadramon was a key plot point (humanoids against beasts bla bla)

But I said in Adventure. In Adventure, her mega is Magnadramon. That’s what I meant. Whether or not it was in Frontier doesn’t make a difference, because in Adventure, her mega was Magnadramon.

Ophanimon is actually one of the Digivolution lines for Gatomon. Magnadramon was the form they used in the 3rd movie, so that's the form that Adventure-Gatomon may evolve to, but even that movie isn't really considered canon.

But in Adventure, Ophanimon was not canon.

In the games and shit, sure, she’s an alternate to Magnadramon in a lot of cases [if our favourite pink luck dragon wasn’t completely shafted because she’s not shippable with Seraphimon WHAT A TERRIBLE MISFORTUNE].

If she had a canon mega form at all, Magnadramon would be it. She was way more appealing anyway, and is one of my top favourite Digimon ever.

EDIT: Also, literally the only reason they had to nix Magnadramon from the evolution table was because she was not humanoid therefore unshippable with Seraphimon. She was a holy dragon, and let’s take the eastern interpretation of dragon into mind when considering the image she brought with her, since she is obviously an eastern dragon. There was nothing wrong with an angel becoming a holy dragon. Azulongmon exists too.

EDIT 2: lmfao I meant to say Goldramon but Azulongmon is a good example of how Digimon actively uses eastern dragons to represent holiness. Basically what my point is, is that Magnadramon was a fine evolution, there wasn’t a need to replace her with an angel.