Problems with this:
1. Doesn't really add complexity
2. Near Guarantees 1 or MORE Summoners a spot in a party
3. Pretty OP really if you consider what you're suggesting based off most in game content (Titan-Egi especially)
4. Once again, giving more reason to go full ranged DPS

I do agree that the Summoner needs to revamped to be focused on the SUMMON rather than DoTs, but your idea has more variables to consider.