Well ... in the beginning there was only 1 Legendary soul you could get (without opening your wallet). That was after beating the beast in madness as far as I remember. G/A souls and Skill Shards were really rare as well ... so when Arena opened the rewards seemed to be huge. Due to the high inflation ... well there we go ...
Instead of tinkering to screw the players the devs really could spend a thought in tweaking other parts of the game to level it with nowadays ...
But as Sparton once said: "Characters make money not new content" ...