Hi there! is fun to review cards before you can actually use them but I really dont agree with your ranking for the summoners.

Tarsa is by far the best and will probably be nerfed before it comes out.

Thaddius in paper seems good but... death splinter already has a lot of way to counter magic attacks. Also if you feel like the opponent will use magic Owster is probably a best option. The card is ok. I think is balanced. Not overpowered but it can be useful.

Quix seems like a pretty strong card just for the -speed wich is pretty valuable.

General Sloan is ok I guess. I just dont see why would you play him when dragon splinter is active and you have selenia to choose from.The fact that all the other life summoners are pretty bad helps this card a lot.

Obsidian Honestly I dont know about this card. In paper seems bad but maybe when we see it in action can be quite good especially against mylor and such. I guess it will depend a lot on the magic cards available for the earth splinter. They only way to know for sure for me will be playing it.

Kelya Frendul This is by far the worst summoner in my opinion. The fact that you can completelly counter him with a 3 mana summoner makes it really bad. I know people are saying "oh but you can make a great combo, you add this, and this and this etc etc"... yeah for sure, you can make a pretty good combo with anything but the card in itself seems underpowered just because is a 4 mana card. If it was a 3 mana card it would be fine. Or even if it was +3 armor.
I mean this card is even worst than drake of arnak. I dont know how anyone can say otherwise. In almost every scenario drake of arnak will be a better choice.