Do summoned creatures ever level up in this game?  or do they always stay the same level and get boned everytime you level up? 
 
I'm asking because I'm level 10 and have the summon skeleton spell that came with my character and everytime I summon it to attack and enemy it get's absolutely raped in combat (one-shotted almost every single time).
 
FYI... I check the wiki and could not find this info.

I don't think they level up because my Ancestral guardian gets destroyed every time in one hit.

I don't think they do. To solve this problem you need to learn new spells to summon more powerful creatures.

No they dont level up.  Eventually you learn more powerful spells, so keep practicing conjuration to be able to learn how to summon more powerful creatures.  A skeleton sucks but you can get Daedra and more powerful skeletons, Skeleton Champions and Heroes.  Careful though, summoning dead shit will get people to say you stink and be all racist.  While I am here, anyone know what the most powerful creature you can summon is?  I keep going back to my daedroth, but even he has trouble now.  Fucking minatour lords are assholes.