I think what this really tells you is that your refurb is not equivalent to a new phone back in 2016, when the reviews were written.
The question is really what did "refurbishment" mean for the battery? They may have just done a quick capacity check and said "that'll do": for example in the UK Amazon "refurbished" devices are guaranteed to have "at least 80%" of the original capacity, but actually if the capacity has dropped to 80% the battery has had a lot of wear (more than it sounds: in my experience phone batteries that report 75% capacity are on the verge of failure). Or they may have replaced it with a third party battery, whose performance will depend on how much they valued finding a good battery vs maximising their profits, assuming there's much choice of parts for a 6 year old phone in the first place. Perhaps the worst option would be if they fitted a "new" OEM battery, because those won't have been made for 5 years and batteries degrade when left on a shelf that long.
So yes, discharging that fast is not good. If you have any right to return the phone (e.g. some countries' distance selling laws mean you have an automatic right to do so for goods sold via mail order within some period after they arrive) then you might want to consider that. But buying a phone of that age, even "refurbished", does carry the risk of reduced battery life.
