I use three rules of thumb:
Rainbow team ( especially your first rainbow 4* / 5* team ) heroes DEF&HP while color stacking ( Empire’s hidden buff ) heroes gets ATT
Game changer heroes DEF&HP while niche heroes get ATT
Heroes that get special skill or talent boost to DEF get DEF, HP get HP and ATT get ATT.
Wu Kong is both my rainbow 4* team yellow and a game changer so he gets DEF&HP
Wilbur is a color stat hero which would normally get ATT, but he is also a game changer so he gets DEF&HP
Ameonna is not on my rainbow team, is not a game changer, Delay works best with matching/ tile damage, special skill boosts caster’s attack and she work best in a 2- 4 purple hero team so she gets ATT, ATT, and oh yeah ATT.
Kage is a solo hero, not a team hero. So most useful on a niche or color stacking team. Kage’s Special is most effective in the first half of a battle. So ATT, ATT … and ATT.
An none of this would matter if reset rules did not make it impossible to experiment, have fun with, or be quirky with class emblems.
Like Boldtusk Delilah is a fighter that can revive four times in a row ( 1 in 123 chance at 5/5 Revive ) with full mana if in Center position. So maximum HP. This boosts both Delilah’s immediate heal on herself and all her minions.
She can heal damaged heroes and give 100% HP heroes minion HP shields so the longer she survives the better her special skill so maximum DEF.