Aqueon probably has good intentions but a 25 % weekly water change is disturbing when keeping any Ray specie. Most of us know It's about the proper wc's not just the filtration.https://www.aqueon.com/information/care-sheets/stingray-freshwater
Thankfully, hobbyists who are at a decent level will take info like this with a pinch of salt. We all know it's about individual nitrate build up which is unique from tank to tank, a blanket statement like aqueons 25% is poor info.Aqueon probably has good intentions but a 25 % weekly water change is disturbing when keeping any Ray specie. Most of us know It's about the proper wc's not just the filtration.https://www.aqueon.com/information/care-sheets/stingray-freshwater
Some with smaller aquariums with a Ray in it will read the 25% as being ok. Your correct with your analysis but not everyone keeping a Stingray has 2000 gallon aquariums.It says 25-50%... 50% a week is sufficient for average ray keepers ie one pearl stingray in 300g of water or a pair in 480g.
I would say that a 25% weekly water change is plenty for one stingray in 2000g of water, so they aren't wrong.