But it makes excellent-but-obscure adventures look bad in comparison to well-known-but-mediocre adventures.Absolutely. But I still find these useful. Not to find the one best adventure for 5E (because that is always going to be subjective anyway), but instead to get a prioritized list of adventures to look into for future campaigns etc.
In particular, the WotC adventures are going to get over-rated since far more people know them.
You would be better running separate polls for WotC and non-WotC stuff. Or have a poll that allows downvotes as well as upvotes.