BvS Impact

BvS was exactly what Snyder intended it to be.

It just wasn't super popular at the box office.

Neither was WATCHMEN or HULK.

I disagree. You are aware that BvS still is the highest grosser (though Aquaman will catch up sooner or later) and the films after it, SS and WW, overperformed. People had certainly become fatigued and cynical about those two iconic characters. No wonder after endless bombardment with films, games, cartoons and TV shows.

BvS with it slow pace and philosophical themes may be an acquired taste but - after Watchmen - it is still the most interesting CBM crime drama post Nolan, more so than the very decent Man of Steel.

Justice League was trash, fun and entertaining yes, but trash, artistically soiled by WB and Josh Whedon with juvenile jokes and cheap cinematography. Suicide Squad was an abomination of the lowest order worthy to be continued by the likes of James Gunn.

Nah, loved it. Deep grungy Rock'n Roll. Boring for kids.

Has only grown since with me. Unlike most movies.

I'd have to agree. It probably did the most damage to the DCEU Brand. It was the most divisive of the movies in my opinion. Say what you want about Suicide Squad, but with the general audience I think most just shrugged their shoulders and said it was ok or different. I don't know if all of it lands on the shoulders of the movie. I particularly didn't like it, but I didn't out and out hate it. The narrative that followed it in the media and online did a lot of damage too. Before the movie The Excitement of Holy Trinity being on the screen together for the first time was massive. Add a little fanboy back and forth. Even with the Batfleck controversy it was highly anticipated. Then World Wide Opening all at one time pushing it high, followed by the movie making Rotten Tomatoes famous, and the second week crash (be it word of mouth or no where to expand). It all played out pretty publicly. Hell my senior citizen Mother asked what Rotten Tomatoes was.

So the divisive movie along with the public media narrative did the most damage, I think.

no - negative or positive spillover effects are often claimed if an allegedly bad movie performs well but the allegedly better follow-up bombs. (Eg the fan backlash against Last Jedi is allegedly one of the major contributing factors Solo bombed so brutally).

However that may be, with BvS this cannot be claimed conclusively as the next film overperformed despite being trash (SS) and the one following hyper-overperformed (WW), being the best reviewed and profitable landmark-CBM. 

Also, the audience scores for BvS are surprisingly fresh, usually around 65, which is ok (not "hated") considering the huge anti-Snider and anti-DC mob downvote factor, and this film is really an slow, acquired taste with philosophical themes but not a easy-listening clobber porn for comic book nerds. Now, compare BvS's audience ratings with the brutal audience score downvotes of TLJ or other recent backlashes as DocWho. 

Conclusions: the data does not back up the OP opinion. BvS film may be considered as the "most boringest" by a certain demographic, but had not the "most negative impact". If any, based on the data Suicide Squad probably had.