If they smart enough to trick Sol, who is basically a god (this could also just be Sol's huge vanity) into wearing the crown AND be able to destroy any of the stars he created, shouldn't they be one of the strongest beings lore-wise ?
The targonian aspects are a magical race that is seemingly one of the strongest forces in the universe(keep in mind Aurelion works for them,that is a lot of power).
They have the ability to posess/merge with other beings and if their host dies,they simply find another one.
is an aspect who has completely taken over his host
& 
get their powers from a targonian aspects
However they seem to have internal problems,which causes their control over Sol to wane.
Magic in this universe kinda just does whatever the writer says it does.
What we know about the Targonians: they're spirit-like, they may have originated on Runeterra but if they did it was before the current wave of known history, they were able to spread off their planet before meeting Sol but it is specifically noted they did not yet have a cross-solar system empire, they were once able to forge things, but for whatever reason they now seem to only influence things by possessing people. It's possible they have ascended to some higher plane of existence, they can blow up stars, they do not like the Void, most of them seem to be assholes, except the Protector, he's cool. And somehow the Targs are linked so that them not being unified has some odd weakening effect on their magic hold over Sol.
We also know Sol is pretty dumb. All things considered. He got tricked by the weaker beings and when he figures out their hold on him was weakening decided to just try to piss them off (which has the potential to unite the Targs) instead of figuring out a way to increase their infighting that caused the weakness and maybe escape.
