leaving out lt and toaa . . .
it would be very interesting. metron said orion may have been the most powerful being in the DCU when he had the equation. he effortlessly took over earth including all its metas. he also effortlessly took over apokalips and new genesis, going so far as to have darkseid prepared to kill himself! certainly no 'heroes' would stop him -- that includes all the top tier guys. he even commanded a promethean giant and in the end used the ALE to destroy a multiversal level enitity that was set to destroy the multiverse!
the thing is, though, the equation controls only LIVING beings. is DEATH a living being? i'm not sure. the only beings that MIGHT be capable of withstanding him would be the highest level cosmics. i'm not sure what defines a 'living' being in the MU. if it helps, even the black racer would have been commanded by the equation.
could he have controlled lucifer with the equation? i don't know. depends on what you think the equation is. is it the antithesis to the source? if so, then maybe it COULD control lucifer.
starlin depicted the equation as an entity capable to effortleslsy destroying dimensions and realities and ultimately the DCU.
it's a very good thread, and in interesting question. i'm afraid most won't know enough about the equation to comment.
imo he very well COULD rule the MU. it really depends on what you think the equation is.