Summoning also has great pairing with a skilled Hydro/Geo party member. The Summoning bonus to received armors synergizes with the extra armours granted from Hydro/Geo passives. The combination makes for an Incarnate that is hard to kill, but still easy to replace.
I don't understand this. Do you mean to say the same character must have Summoner and Hydro/Geo?
The same player doesn't have to, but it would improve the armor granted from Infusion abilities.
If the Summoner has points in Hydro/Geo then Farsight/Power Infusions grant more armor, respectively.
If any party member casts Fortify or Frost Armor on a Summon with Soul Bond then it will also grant more Amour than listed by the ability tootlip (due to Soul Bond).
E.g. if the Summoner has 10 points in Summoning then any cast of Fortify on their summon (even by other party members) will grant double as much armor as listed.
If the caster of Foritfy has high Geomancy already then the Geo passive improves their amount, then Soul Bond improves it again, for a ludicrous amount of armor.