Yeah that can obviously happen that you might already be running on the fastest RPC node...I only changed mine once to a node that was only a little bit quicker, and I tried running another benchmark to see if any of the others were faster like a week later, but ended up getting the same result as you- the api.hive.blog node was/is the fastest one that I can run on...I just know that one or two people had mentioned that little trick back when splinterlands was like really slow & laggy a week or two ago. & because I do use hive keychain extension on my splinterlands account though, so it did have some effect at first..albeit very minimal. Always worth a shot though..🤷‍♂
Sorry I couldn't help out more!