I’ve always been baffled by how people at WB hold that opinion. Sure, it’s fine for random, casual fans to think Superman is boring or that Batman should only be "realistic" and "gritty". It’s expected that casual fans won’t know beyond a surface level. The issue is that the people making these movies, and the ones calling the shots, are dumb enough to think the same. I facepalmed hard when Snyder said so, and he was the lead of the DCEU.
WB and DC aren't exactly known for their great management.
In saying this, a large issue for DC compared to Marvel was how well known their characters were/are in pop-culture, and how that unfairly breeds stigma against them.
I think Robin and Aquaman are the best showcase of how classic DC really ruined 90-00s adaptations. Aquaman has consistently felt like a compensation character because everyone threw shit at him due to the Super Friends. The only Aquaman that has felt genuine is Brave & The Bold, will also give credit to Mamoa for being mostly fun. Every time they try really hard to make him a super badass.
Robin was the butt of 500 gay and pedo jokes, making every Batamn writer avoid him in adaptations. I will actually give Warner credit for forcing him into BTAS, otherwise, Timm and Dini took the Robin sucks stance and would have left him out. It really wasn't till Teen Titans 03 and Young Justice (2011) that Robin suddenly became the coolest DC character.
Superman and Batman are products of their adaptations. The Donner Superman films got hijacked half-way through and derailed Supes into the lame duck of today. Sadly, STAS was not prominent enough to save him, especially since every film after would be a dud and Smallville is Smallville. Nowadays Injustice is the most prominent story Superman has, unfortunately.
Batman, as stated before, got screwed by West, saved by Burton, screwed again by Schumacher, then saved by Nolan. Now we are stuck with Nolan