Formal alternative to bullsh-t
Solution 1:
I see two useful approaches here. First, something like "Everything he says is unfounded," or "His whole essay is incoherent." These two suggest Bob is making a weak, ineffective argument. From Collins Dictionary:
If you describe a rumour, belief, or feeling as unfounded, you mean that it is wrong and is not based on facts or evidence.
If someone is incoherent, they are talking in a confused and unclear way.
If you say that something such as a policy is incoherent, you are criticizing it because the different parts of it do not fit together properly.
Incoherent - Collins Dictionary
Unfounded - Collins Dictionary
If you want something a little more directly critical but still formally phrased, you could call his bullshit "empty rhetoric." This suggests he's deliberately using linguistic tricks to obscure a lack of content. That's appropriate for a formal register, but it does come across more like accusing Bob of deliberately bullshitting, rather than simply failing to make a good argument.
Collins again, 'rhetoric' definition sense 4:
- speech or discourse that pretends to significance but lacks true meaning
Rhetoric - Collins Dictionary
Solution 2:
"Nonsense" would be my first choice too. "Absurd nonsense" is even stronger.
"Nonsensical" might be a good choice too.
Nonsensical: If you say that something is nonsensical, you think it is stupid, ridiculous, or untrue — Collins Dictionary