> To just give one example, there are a ton of places you can choose to throw in an o- or not, just like in English, you can choose to say "the" or not.

Definiteness marking is certainly an area where speakers of languages that don't do that get confused. But I'm not comfortable saying that there are a ton of places in English where you can choose to say "the" or not. In most cases, there's only one correct choice.

Going back over the nouns in my previous paragraph: (marking area[0] speakers[1] languages[2] I ton[0] places English you cases choice[1] [there])

[0] rival article already marked

[1] "the" permissible; presence and absence are both fine

[2] "the" possible; presence may raise eyebrows