Level up your hero, get better gear, summon more troops, level up your troops, your spells, anything, and you have more damage. Moreover, there are already plenty of units following the hero - one more pet unit would make close to no difference, except it was as strong as a hero, which would be quite pointless: A hero is the hero because he is the one super strong unit.
Moreover, the strength of attack and defense is quite balanced now. A major attack buff would just ruin that and make winning attacks way too easy - so why would you even need additional damage? If you are too weak to beat a certain player P, attack weaker ones and wait until you are stronger before you attack P again - or just try a different strategy better fit to his weaknesses. Everyone - even top 10 players - fails every now and then, or has to scroll in order to win - if he attacks relatively strong opponents. And everyone can and will win battles if he uses strategy and attacks opponents that fit to ones own hero/troop/spell strength.
To be a useful addition, a pet would have to have other functionality than just “some extra damage” that can be achieved in various other ways, too…
Please not that if you can come up with some actually useful and interesting functionality (that fits the rest of the game) for such pets, I won’t just categorically refuse it, but without such functionality we definitely need no pets, as there is already enough to do and enough to run around our hero right now. And if you want something strong and fluffy, summon a werewolf
Of course, and you know everything.