basically i dislike batman: the chalice because it demonstrates a poor understanding of both the real life history of the grail (well, "real"... as we all know i am adamant in the belief that no such vessel ever existed, or if it did then it has not been preserved), and a poor understanding of arthurian canon... though since it alleges that the waynes are descended from sir gawain, the 2nd one is wayy more important.
it also posits possessing the grail as "cool", when... i don't think it is? like, in order to be worthy of it you have to heavily adhere to medieval codes of chivalry (which are of course incredibly christian), and doing that in the modern day is just lame. actually it's not just the medieval chivalric codes--you have to be christian to a truly ridiculous degree. these days that's not really seen as admirable, just stuffy at best
(though to be clear i'm not complaining. i like modern rules of politeness just fine.)
it's also just disrespectful tbh. like why is batman a grailkeeper when he's barely even christian*
(*i know he's nebulously jewish but afaik he himself has never been portrayed in canon as jewish despite participating in christian traditions such as christmas many many times. also, this was published before that)