Why choosing a (canon) character is FLAWED

[Amaterasu]

The thing with a canon character is that you are given a pre-made character, possibly with art, but with a personality, looks, relationships and so on, meaning that while on one side sure your creativity is inhibited because you aren't making your own character, on the other side you have a well-made character to work with already.

The instant that you bring that character into the Omniverse you are faced with a new situation and nobody is telling you how to play them, there are no rules saying that the character must be played canonically. Your creativity is moreso limited by your self-imposed limits (of wanting to play the character canonically) than by the character themselves - because like said nobody will insist that you play your character a certain way. Playing a supervillain as a friendly hero or vice versa is completely acceptable in the Omniverse, and would at worst get you a few odd looks.

A canon character is mostly a crutch, in my opinion, because they give you premade art and story to have an established character that you can take onwards, rather than starting from scratch. Some people work better with OCs though. There's no real right or wrong, it's just whatever works best for that specific person.