Believe me I am being kind 
I’ve hosted (and played in) a lot of games over the years, starting in civ5 times more than 10 years ago and now in civ6. There are many kinds of games that can occur, and certainly the simplest is when everyone picks their own civ/leader and we all get to it (and believe me I am currently wishing we were doing exactly that, rather than arguing about whether various players should get exceptions to the rules agreed upon in advance). However, many players feel on certain maps or under certain game conditions (with good reason) that there are inherent inequities in the game they would like to see minimized or balanced, and a frequent way to do this is devise some system for assigning civilizations & leaders to players other than player choice. This is one such game. I assume this is primarily because it is a True-Start-Location (TSL) map, which means that the map itself has much more inequality baked into it than a normal civ6 map is likely to have, and in addition civilizations will start at their historically ‘true’ locations, so that inequity of geographic opportunity will be distributed unequally by civilization.
In response to these concerns and as you can read above in the earlier posts, the draft and then player choice system was negotiated and agreed to by a majority of the players in the game. As I’ve expressed many times, I’m open to negotiating a new set of rules, but I’ve learned painfully from experience and observation that dealing with these questions inconsistently as host is a recipe for, as you say, ‘killing the fun.’ If you get to pick by player choice but everyone else has to abide by the rules accepted by the majority, this is a recipe for disaster – other players who participated in the discussion above in good faith may leave the game, for example.
Having said that, I’m not sure you’ve thought through the implications of Kupe on a TSL Earth map. You would spawn in the ocean east of New Zealand, and given that @Pete has selected Australia and will spawn on the east coast of Australia, you will find yourself in a challenging position. In addition, SE Asia will be essentially open for either yaboo (Gandhi) or Randomouse (East Asia) to swallow up early without real opposition. This question of the balance between Pacific Islands and SE Asia was considered above – and certainly we can consider it again, revise the lists and rerun the draft (or decide as a group not use the draft at all and go with player choice, for example).
You say you’re a newish player – have you played Ba Trieu or Jayavarman VII? What makes you think they would not be fun to play? There will be many other games you can play Kupe in, but in this one a set of rules has been agreed to by a majority of players that the civ options available to you are set by a random draft.
I did not start this game so I could play Mali in western Africa – frankly I’m not personally overjoyed that I drew the Mid/South Africa list. But, I agreed in advance to these rules, which I participated in good faith in negotiating, and so I am following and enforcing them. It’s been my experience that the most fun and rewarding games are often the ones that are not a direct result of my choices, but rather the ones in which I am challenged, as in life, by circumstances not of my choosing and must do the best I can to rise to the occasion.
Now, if your heart is set on playing Kupe in this particular game and that is the reason you joined, then sadly this game is not a good fit for you. If you host a game in which you play Kupe on this map, I’d gladly play in it with you (and I’m guessing many of the other players listed here would happily join that game as well). If you’re unsure about hosting, and want to play that game, I’m happy to host that game separately from this one under an every-player-chooses-first-come-first-serve rule. But I’ve agreed in advance that is not the set of rules for this game.
Personally, I hope you stay and take a chance on this game – you never know, it may surprise you.