No, Batman isn't toxic.
On the one hand, DC has turned a hero who used to be -barring campier interpretations- a noir detective/ pulp vigilante (a Sherlock Holmes/Zorro fusion of sorts) into, paraphrasing myself, a character who -despite his so-called "realism"- has learned every imaginable knowledge and mastered hundreds of martial arts before his thirtieth birthday, can kill gods with enough preparation time because he's always eighty steps ahead of everyone and everything, can build every imaginable device/vehicle, can dodge bullets and heal any injury overnight even although he hardly sleeps, and he has no issue running his billions-worth business.
Batman IS what Superman haters BELIEVE the Man of Steel to be.
DC has consistently put down and neglected all of their remainder heroes and villains in order to prop Batman up and please "Batgod" fans. As a result of it, their universe seems considerably smaller and more insignificant, their characters look less interesting, and Batman is their only reliable high seller.
On the another hand, fictional characters aren't to blame because of editorial mismanagement and stupidity. Batman is an iconic character as proved by the fact he has endured the test of the time and survived several nearly-cancellations before finally finding long-lasting success. He shouldn't take the blame for DC's greedy, dumb policies that are wearing him out at the same time that ruining other characters.
Moreover, I'm sorry to say Isabella sounds like a resentful fanboy. Undoubtedly, DC could have pushed Black Lightning better, but It isn't their fault that Black Lightning isn't as popular as Batman.