Prices are To hight (in relative terms)

[Niwashi]

bolded the parts that can be taken as first come first rewarded. The idea of a first place prize loses its meaning when multiple people strike the same part

If you think that just the fact of naming it "first prize" means there's only one, then the same would hold true of "second prize", "third prize", and "fourth prize". Yet the game explicitly describes the conditions for each one, and those conditions don't involve the luck of other players. There may or may not be multiple players who get all four numbers right, but there's certain to be lots who get just the last number right. Do you think that that fourth prize gets divided between all of them? Or that only one of them gets anything?

a tie in the chocobo races has both players in 1st gain the same experience and MGP as the 2nd place, meaning in truth there is no first person.

The chocobo race is different, because it is a race. That's the nature of races, that your result is measured in terms of how you place among the other contestants. So that has the concept of a tie, and therefore SE has to come up with a way of scoring ties.

In jumbo cactpot, the score is how many of the four numbers you get right. Other contestants don't affect your score because other contestants don't affect how many of the four numbers you get right.