The shield didn't interrupt the flow much, it was a gag that rolled straight into it being almost literally a paperweight. Whereas Flash was forced in your face screaming at you, look at me, look at me, look at me, I'm important! Except not really because what exactly did my message do to any aspect of the movie I was shoehorned into? Was Lois ever in danger that Superman couldn't save so Bats had to? Why was she the key? And the key to what? And what was Bats supposed to do differently than whatever future version of himself did that Flash was supposedly warning him to do or not do?