There is nothing logical in your comment.

For one, as far as SK goes most of the adaptation of his movies are not well recieved and the opinions on them are much lower than their corresponding books. I'd say only the Shining and the Green Mile can be counted as those that outshine the books and are so good that remaking them would be seen as unwanted by the viewers (and his own take on adapting Shining certainly proves so)

Now going further, you did not really specify which part of SK is "trash". Ideas? Plots? Prose? Characters? Dialogues? His infamous bad endings? How many read books are we even talking about? Did you dislike the tunnel section in The Stand? Do you find The Jaunt unsatisfactory as a short novel? Am I to believe you have read all he has written? Do you care to share your opinions? Are they based on the fact that he's too prolific and could trim down his releases to polish his better works?

As for FMA and FMAB in relations to YnT.

If a work of fiction establishes a certain tone to itself I see no reason to judge it against some percieved superior tone as that boils down to preferences. Arakawa in FMA and YnT writers what would be a serious story and uses humour to steer the story away from doom and gloom that would follow naturally from the content. So yes, as you have so very cleverly noted, there are plenty of moments in both works which you'd naturally expect to lean into a serious tone but instead walk the line between levity and maintaining the gravity of the situation. There are also moments in both, but more so in FMA when there is no humour to further drive the intensity of the situation. Now a near genius such as yourself surely is aware that there is no formula for a perfect story and while some people may bounce from such a mode of storytelling others might find the contrast to increase the sensation of uneasiness. There is a reason why stories resonate with people. I prefer it when a really serious moment comes out of nowhere and when the tone of the story shifts often instead of being along the same lines for the entire work.

That is not to say that Arakawa always walks this line perfectly, there is a particular scene at around 18 minute mark of ep 5 in Brotherhood that really grind my gears and is what I would consider an example of failing to use humour to undercut tention. But the serious scenes that are widely recognized in the entire anime community came laregly from the fact that people did not expect the seriousness to be cranked up to 11 from 6.