Fair enough, what I should have said was I think it isn't core because a sizable enough body of the gaming community doesn't engage it. To me it is a non-essential feature of RPGs. RPGs can be totally serviceable with bad writing. You don't need good writing to play them. Generally you need the other core elements of the system (though there are exceptions of course, like with combat if a group simply never has combat encounters).Wrong it is core (see how easy it is just to declare something).
As to the rest of your post yeah you are choosing to downplay a particular element of roleplaying games that you don't care about... doesn't mean it's not core and it doesn't make your preferences bad. There are people who engage very little with the combat engine when running games of D&D... Is combat a core feature of the game, yep. Does this make their games any less D&D? Nope. Does it make their games bad? Nope. Can they now declare combat isn't core to D&D...
I don't think the element of good writing is core in the way combat is though.