User blog comment:IamJakuhoRaikoben/Chapter 433 & 434: Ikusatsunagi & Demolition Fist, Review./@comment-1776824-20150512000613

So far, all I am gathering is that the only legitimacy people are putting forward is that Ikusa-Tsunagi was quote-unquote "weak" because Arlock didn't have much power. Although we were told that the strength of a summon reflects the strength of its summoner, the actual chapter says something along the lines of that as a Mage grows stronger, so do their summons, meaning that they have their own base strength, and that they can grow stronger by feeding off the power of their summoner. You have to think, a summon can't be as strong as their summoner can, otherwise every single Spirit Lucy had in the beginning would've been weak. Loke would've lost power, because his presence when summoned (by Lucy, when he summons himself it is clear that he is using his own strength) is due to him siphoning off Lucy's Magic Power.

Let's take a look at the Spirit King. He is a fucking beast, and the only reason he even left was simply because he most probably figured Mard Geer wouldn't have been able to escape from that prison, and his only real purpose was to save everyone because Lucy just couldn't at that time. If the Spirit King's power was relative to Lucy's magical strength, then the Spirit King would've been wasted in one hit and Galaxia Blade wouldn't have been a thing.

This whole summoner strength = summoned being strength is just ridiculous. At best you can say that if a summoner can summon something of great magnitude, then it is at its normal, base strength (and for a "God" that should be absolutely monstrous). If the summoner is extremely strong in terms of Magic Power, then the summon has more to work with outside of its base levels and can temporarily gain more power as long as it is linked to that summoner, because Spirit Mages are essentially summoners, and its a great explanation for how this type of magic works.

I know that people are going to comment with something along the lines of my explanation is stupid, or with another counter example saying how I'm wrong, but this is just how I am interpreting it. Natsu straight up killing a freaking God in one hit when there is a magic dedicated to this purpose, when he has already done all the stuff Carry said below, is just absolute garbage. RIP Ikusa-Tsunagi. You were worthless and its not your fault.