I get what you are trying to say. Just when it comes to this game, belief and assumptions derived from commendations or how progress is handled is really bad for the soul and will get you angry and confused in the future.
Ask Rare during their streams if Arena is meant for PvP and they will deny it saying that Arena is not the PvP server and that its strictly a condensed version of Adventure.
A lot of players think "oh well this was released and so that means that Rare really wants this!!" then when players don't get their way they get mad at the community.
I just don't want to see you go down that rabbit hole and get stuck in an argument over implications and assumptions.
Trust me I get what you are saying. How the hell is Arena not the competitive option of SoT when Rare is using it to hold competitive tournaments. However, then I realize that players have been doing wonky stuff in Adventure as well, holding races, game show like contests with rewards and what not, and I think I heard of someone holding hide and go seek games??
Knives can kill people but not all knives are used to kill. A kitchen knife is created with the intent to be used for culinary purposes, but if someone used it only for killing, that doesn't change the fact that the knife's original purpose was for cooking. - Basically speaking the mode was created with the intent to give players who had a limited time of play time a chance to play the game. How we use the tool has no bearings on the actual purpose of the tool.
Don't trip and fall into that rabbit hole my friend. Its a dangerous place and will make things more difficult for you in the future.