First
It would be cool if Leggylass came in a rainbow of colors, not just green.
Second
Make DOT 1 turn would make it better for the hero’s owner.
Third
This comes back to the question- Why cannot all heroes be good?
Answer- most heroes are based on Boss mechanics and few people want Vampire Lords ( Sartanna) with 1 turn DOT or Dragons ( Azlar ) with very fast mana.
Most HotM have fast mana speed, because fast mana speed is king. But Gravedigger ( very fast mana with 2 turn DOT ) is a HotM that you can skip in raid/ war by not attacking. You will have to fight Lady Locke every 3 months ( current schedule ) or 5 months ( future schedule ) if you want the Challenge event rewards.
Some heroes are good, some suck, most are in between. Same with the bosses they are based on.