Other than "accidentally" making stars go supernova during their civil war, the Q never demonstrated the kind of absolute power one would expect from so-called "omnipotent" beings.
Most of what they did could be boiled down to:
* Implanted mass hallucinations.
* Varying levels of psychokinesis.
* Interdimensional travel.
* Clinical immortality.
There are nominally human superheroes who can do the above, either biologically or through the use of technology. The Q just don't seem all that powerful by comparison.
And hey, even lame-ass corporal mortals can blow up stars on command. Ask Tolian Soran.