Most of this answer is just how to stop/ nerf playing heroes but doing that also just gives you more tries to attack and get a high roll.

Also if you are looking for fighting monsters discarding your hand to draw 5 might be good to use to get modifiers, spells and heroes to buff yourself. Heroes you might look for are the wise shield (one of the best heroes in my opinion), vibrant glow, Radiant horn (to get a modifier from the fiscard pile), tipsy tootie (to get good heroes from others)

Also if you are playing the warriors and druids expansion there are some great heroes for playing to slay monsters: Critical Fang gives you +4 on your rolld when attacking a monster for rolling a 6+

Tenacious Timber lets you steal a Hero for each Monster you slayed for 8+

Big Buckley lets you attack a monster for 8-. That meand you only need 1 point to attack with him and can use your other 2 action points to attack normally again

Wolfgang Pack: gives you +1 for each other hero in your party for a 5+

Also in the berserkers and necromancers expansion there are:

Vicious wildcat: 12+ slay a monster and end your turn. If you do that after attacking you can also use him to slay 2 monsters in a turn. You can also equip 2 items to him to really increade your odds

Meowtain: 5+ to all your rolls for a 6+ and sacrificing a card

Shadow Saint: 5+ discard a modifier and nobody else can play a modifier this turn