Most people already do what your saying.
They do this philosphy with heroes who do Ally Protection.
Ally Protection redirects incoming damage.
For Example:
Jareg does Ally Protection.
Ally Protection is a buff which goes on 3 teammates excluding Jareg.
When the 3 teammates get attacked, They don't take the full damage.
Part of the damage is redirected to Jareg.
Ideally, you want the heroes who have the Ally Protection buff to be high DEF.
High DEF allows them to mitigate the incoming damage
Let me give you some numbers to help make sense of the situation.
Lets say the enemy is attacking you with 1,000 Damage
Lets say you have 0 Defense
Your hero will lose 1,000 Health because you have no Defense to Mitigate the incoming damage.
Lets say the enemy is attacking you with 1,000 Damage
Lets say you have 2k Defense which Mitigates 50% of the incoming damage.
Your hero will lose 500 Health because you have 50% Mitigation
Lets say the enemy is attacking you with 1,000 Damage
Lets say you have 2k Defense which Mitigates 50% of the incoming damage.
Lets say you have Ally Protection Buff on your hero
Your hero should lose 500 Health because you only have 50% Mitigation
However, the Ally Protection buff will split the damage among 2 different heroes.
The Ally Protection Sender (Jareg) will lose 250 Health.
The Ally Protection Receiver will lose 250 Health.
For this reason, Players like to run 1 high HP hero with 2 or 3 high DEF hero's.
The perfect situation would be 1 high HP + 3 high DEF.
However, Players have tried other set ups which have worked.
They have done 1 high HP + 1 high ATK + 2 high DEF
They try to squeeze in a Squishy Attack type Damage Dealer who can do massive damage.
Another set up which people have tried.
They have done 2 high HP + 2 high DEF