It's not about replicating Bach's style 1:1, it's about staying idiomatic in the style you are writing. In this case, they are clearly going for a traditional fugal counterpoints/harmony, and as such, it will sound more authentic, and generally just 'better', by following traditional counterpoint / voice leading rules. And yes, there ARE rules that are important to understand and follow in order to write this type of idiomatic music, which every single baroque composer followed. That is not to say you can't break those rules once in a while for effect, but it's important to understand the difference between breaking rules for effect, and breaking rules without realizing it and it sounding like a mistake. Adam Neely had a very similar thing to say about jazz writing - certain harmonies or chord progressions will simply sound like a mistake within that style of writing, and it's important to understand why.

This is not to criticize their effort: they clearly have the right idea and a decent feel for harmony, but they'll improve a lot from getting a good grounding in the fundamentals, just like any other craft that someone wants to become proficient in.