me_irl

Yes, "on point" is slang, but only just recently. Slag is just a little further down the scale in terms of specialized language.

The real test is how accepted a word or phrase is with the larger population using a given language (while keeping a specific meaning in mind). This gets a little muddied with the lingo used by larger groups.

For instance the phrases "weird" and "cat lady" have both been co-opted by the major political parties in this election to decide their opponents. Because they each have so many members and because their discourse is covered by media outlets the new connotations of those phrases will be more widely known outside of the group and will stop being lingo much faster than the phrases you use privately with your family or coworkers.

"On point" used to be lingo in the military once upon a time, but because of the size of the military (and aided by the internet) it has become slang and is no longer a phrase only used by a certain group.