I consider this a truism with no basis in anything more than having given up on the publisher.
To me, this mindset says "since D&D has been terrible at providing robust high-level support for decades it must be that this is impossible to provide. Thus, TSR/WotC are blameless for not even trying."
Bollocks.
Of course you can provide robust high-level support. For starters, have NPCs and monsters actually be competitive with actual player characters created using nothing but the tools given by the PHB. Of course there will always be variance, but that fact does not excuse setting the baseline at "pathetic". I understand the desire to keep things simple for beginners. But that excuses only so much. A CR 5 critter with no special abilities? Fine. A CR 15 without any enablers that gives it a decent shot at delivering its main attacks agains competent players? That is indeed pathetic.
So that's a given.
You could actually engage in a discussion about expected character abilities, instead of sweeping them under the rug - or worse dressing them up. If you state things like "we expect a front-line warrior to do an average of 45 DPR and have an AC of about 20." then that tells you what you really truly need to know, as opposed to giving you a load of horse crock about "expected encounter levels" and pseudo-scientific-sounding "encounter difficulties". With hard numbers you don't have to guess! You don't have to be bewildered why your heroes cuts through the BBEGs minions like butter. Instead you simply go "oh, this adventure works best when my party is 4 levels higher (or lower)". One group might do alright at level 13 where another group needs to be level 19. But this is (to 90%) determined by real numbers for offense and defense and certainly no made-up BS calculations.
Then just add robust tools for managing the mountains of gold official adventures heap onto the heroes (not by removing the gold, but by allowing heroes to spend it on things with immediate use in further adventures aka magic items) and you're basically done. Or if not exactly done, at least in way better shape than any official so-called "support".
So no. I will keep characterizing WotC's current efforts as weak-sauce to newcomers because I know they could do better, thankyouverymuch.