There's no grammatical rule that I know of that says you can't have orphaned adverbs like this. As a general rule of thumb people tend to over use adverbs so limiting that may be desirable in a stylistic sense.
I think the bigger issue here is that the phrase "more conceptually" doesn't make sense in this context. What thing is more conceptual than what other thing? My understanding of the sentence in a literal sense is: "To understand this phenomenon at a more conceptual level [as opposed to the nuanced one above] it is useful to remember that a heavy cow will move more slowly than a lightweight butterfly."
I think that you would be better served by saying
"More simply, the heavy cow..."
"In short, the heavy cow..."
My personal preference goes to the second because fewer adverbs but that's 100% stylistic.