Or you can get a character to level 65-75 and fight the real avatars with a party. Whether it be level 20 solo with only carbuncle, or level 65+ with a team, getting these avatars that parties won't even let you keep out is quite a challenge. The summoner class has the hardest time being anything but gimp compared to any other class, and the summons you get aren't strong enough to be worth it till incredibly late in your chr's career.