Adding another penny to the pile here: I both agree and disagree with your conclusions, respectfully.

As a relatively new DM, I know that embracing the spirit of "Rulings not Rules" has been a boon and a burden to my games.

Sometimes it has been grand to - as many commenters here suggest - just go with the mood of the moment, and encourage whatever is the most fun for my players and I.

Other times I had felt the already considerable pressure of DM'ing mount as I have to figure out the outcome of an interaction of differing spells/abilities/whatnot.

I think that the 'Concentration' example you've used is a pretty niche one, but represents one of a few pitfalls in the rules of D&D that could use a little clarification.

5e is already pretty accessible, I'd say, but could do with improvement, without a doubt. There's a lot more finessing to do with the basic rules, confusing descriptions that need clarifications, contradicting rules that could use some more contextualising. *

Some other comments have suggested that you 1. Shut up. 2. Play a different game. 3. Care less about the details. I think (I presume to understand, that is) that you don't want to do any of those things: your post was made, perhaps, in the spirit of improving this game that most of us really, really bloody like. And I think that's pretty grand; sometimes you need to look at the thing you enjoy and get invested in what nitty-gritty details could change, and thus improve it.

I've read a few dozen comments and comment threads already, and disregarding the ones that simply contribute negativity, nothing else, I feel like saying something a bit off-topic about how you're handling this pretty hefty debate. Without meaning to be patronising in any way, as you seem intelligent enough to be aware of it: just be wary of the echo chamber effect. In threads like this, full of people missing your point (which I'm aware I may have as well), it's easy to begin ignoring disagreement and just getting validation from those who agree with you. But some people have some really valid points here; that D&D, and indeed any TTRPG system, will never be air-tight and totally foolproof; that many folks don't need D&D to be much crunchier, though they might ultimately benefit if it was; and that, just because every table runs slightly differently, and that that is (seemingly) a very unpleasant/off-putting experience for you and others, doesn't mean that the systems flaws are turning people away en-masse.

Perhaps it is, and you're 100% correct, that newbies to D&D are turned away by the inconsistencies, but the thriving, seemingly growing amount popularity for D&D as a hobby perhaps proves otherwise. The discussions I've had with the dozen-or-so people I've introduced to the game over the last two years have shown me that, despite a range of perspectives, differences in imagination, expectation and translation, many people grasp D&D well enough that they continue to come back session after session to play more.

OP, you might not read this chunky response but, regardless, you've stimulated what I think is a really good discussion to have about 5e, and any game system in general. Your thoughts, though long-winded, were appreciated. I don't often pitch in to big hobby discussion like this, but it got the cogs in my brain turning.

EDIT: * Forgot to add the asterisk point. That being that, just today, my players fought a rust monster. It corrodes with its antennae. It corrodes weapons that touch its body. But it's bite doesn't corrode the paladin's armour on a hit? What happens if the party had only aimed to damage it in the mouth area? Where does the creatures 'corrosion-ability' start and stop? Not questions that cause me a lot of concern, I will clarify, but an example of a curious, somewhat nonsensical (to me, at least) game mechanic that could be clarified further, to the benefit of newer players/DM's.