It really made me uneasy, to think that formal communication might start getting side looks.
Probably 5th grade, but your comment is directionally correct.
I work at a college for fuck's sake.
This will be a cat and mouse game. Content factories will want models that don't create suspicious output, and the reading public will develop new heuristics to detect it. But it will be a shifting landscape. Currently, informal writing is rare in AI generation because most people ask models to improve their formulations, with more sophisticated vocabulary etc. Often non-native speakers, who then don't exactly notice the over-pompousness, just that it looks to them like good writing.
Usually there are also deeper cues, closer to the content's tone. AI writing often lacks the sharp edge, when you unapologetically put a thought there on the table. The models are more weasely, conflict-avoidant and hold a kind of averaged, blurred millennial Reddit-brained value system.
It's been two years now since such commonly agreed upon signs appeared yet by and large they're still just as present to this day.
“Most times A happens before B, but this order it’s not guaranteed. Therefore, there is a possibility of {whatever}.”
Alternatives that come to mind are “as a consequence”, “as a result”, “this means that”, but those are all more verbose, not less.
A simple “so” could work, but it would make the sentence longer, and the cause-effect relationship is less explicit I think.
"Most times A happens before B, but in this order it’s not guaranteed, so there is a possibility of {whatever}."
I could see arguing that starting a sentence or paragraph with "Therefore, " repeatedly in one essay is empty but tbh your teacher just sounds jaded.
"He didn't send the letter. The lawsuit was dropped."
"He didn't send the letter therefore the lawsuit was dropped."
Two very different examples. "therefore" in the second example communicates a causal effect from the independent clause that isn't present in the first example.
I'm sure one could argue that context clues could imply that same connection and therefore "therefore" is redundant but I just don't agree with the premise.
As an example, here's what you original statement said (with some grammar corrected):
"Most times A happens before B, but the order is not guaranteed. Therefore, there is a possibility of {whatever}."
Here it is if you lead with the important outcome and provide the justification after, using a non-restrictive relative clause to add the fact that A often happens before B:
"There is a possibility of {whatever}, as, while A happens before B, the order is not guaranteed."
In my opinion, this is clearer in intent. It provides the important information immediately and then justifies it immediately after. The original sentence provides information without context and then contextualizes it using "therefore", which comes across a bit pedantic to me. I am a native American English speaker though, and the tone of prose does vary depending on the culture of the person reading it.