did i get this right?

That is mostly right. At least your definitions match the definitions I use. But pan doesn't mean "50/50". You are forgetting about non-binary people there.

Omni means that someone is attracted to people of all genders, but not necessarily in the same way or amount. If we settle on your definitions of bi and pan, it is basically a new word for bi. People often think that bi doesn't include non-binary people (or even trans people in general). If someone uses the word omni, they make it unmistakably clear, that they include non-binary people in there definition as well.

An this is also why dictionaries give bad definitions. The word bi has a long history, but luckily society changed. For example trans and non-binary people get more recognition now than 20 years ago. Some people feel that they need to create new words while others think, that the old words already meant the right thing or believe that the old word should be used in a broader sense.

/r/bisexual Thread