Student or Learner
is it bad to use the word "Rather" to begin a sentence?
Ex. Rather, the relationship between early horticulturalist and foragers most likely involved connections which constrained and shaped the decision making process of both
No it's okay. It's just that some English teachers find that students too often begin with such conjunctions, so they try to improve your style by telling you to avoid them. It's a judgment call, but this example is certainly not wrong.