The reason rulesets for summons and NPC minions and the like seem unfair is because you're forgetting that Arena fights are inherently 1v1s, if your minions (of which you usually have multiple, and even with just 1 your character included makes 2) were overly formidable it would be unfair on your opponent. All of your minions (And your character themselves) have to add up to the tier you're at, which will usually be your opponent's tier, so essentially all of it included has to be equal to your opponent.