Actually, they're textual analysis, much of it comparison of the earliest versions of the texts to what they say now. then he analyses how the differences may have occurred.
You may not like his conclusions, but they're based on much more substance than "unsubstantiated speculations and wishful thinking."
Actually, Higher Criticism starts with a presumption, then filters every “analysis” through that. You might not like the fact such analyses are premised on bias and thus inherently flawed, but this is contrary to objective historical documentary analysis. Dig a little.