The Brotherhood of Saint Traft

I was reading through the Daily MTG article when this one caught my eye. Particularly, I liked the mechanics behind the card. To me, the summoning of a creature as beautiful as an angel would be an awesome way to fight. So i have tried to convert Saint Traft as a divine Patron for Pathfinder Rules.

Brotherhood of Saint Traft
When criers brought news to the various town that the famed demon slayer was dead, many thought that this was another nail to the coffin for Innistraid. With Ashmouth unguarded, the people fear that the demons would come in hordes and would run amok the already doomed land. As despair descended upon the people, a group of clerics organised themselves in the name of Saint Traft. A priest named Marco had found the technique to call down the seraphs as Saint Traft had. Marco taught it to the Brotherhood and asked them to spread the word. The Brotherhood now runs around, teaching those who are strong in their faith the technique and avenging Saint Traft with each thrust of their sword.

Below are the archetype for the clerics that are in the Brotherhood:

Champion of Saint Traft
Calling upon celestial forces, the Champion of Saint Traft leads the charge against evil and vow to never rest until the last demon is killed.

Alignment: Any Good

Diminished Spellcasting:
A Champion of Saint Traft chooses one domain from his deity's list of domains and gains one fewer spell of each level than normal. If this reduces the number to 0, he may cast spells of that level only if they are domain spells or if his Wisdom allows bonus spells of that level.

Summon Celestial Forces:
Starting at 1st level, a Champion can cast summon monster II as a spell like ability a number of times per day equal to 3 + his Charisma modifier.At 6th level, and every 5 levels thereafter, the power of this ability increases by two spell level, allowing him to summon more powerful creatures (to a maximum of summon monster VIII at 16th level). At 19th level, this ability can be used as gate or summon monster IX. If used as gate, the Champion must pay any required material components. A summoner cannot have more than one summon monster or gate spell active in this way at one time. If this ability is used again, any existing summon monster or gate immediately ends. These summon spells are considered to be part of his spell list for the purposes of spell trigger and spell completion items. In addition, he can expend uses of this ability to fufill the construction requirements of any magic item he creates, so long as he can use this ability to cast the required spell.

This ability replaces Channeling.

 Sacred Summoning:
At Level 1, the Champion gains Sacred Summoning as a bonus feat

At level 5, the Champion gains Augment Summoning as a bonus feat. At level 15, the Champion gains Superior Summoning as a feat.

At level 10, the Champion's summon gains an additional +2 to Strength and Constitution. This is in addition to the bonus granted by Augment Summoning. At level 20, the bonus increases to +4.

The archetype i think could be used for different settings ( I think). I gave it a more summoning bent as several of my players have wanted to play such an archetype.Give me your comments on whether this is unbalanced or overpowered?