2024 really is a clownshow, geez.
For sure, though not (strictly) for that reason.
The bigger issue is that 5e, regardless of .0 or .5, simply doesn't bother even
thinking about math when you're talking about CR 27 creatures. Like, by CR's own self-description, no matter how inaccurate that description may be, a "CR 27" creature is meant to be a comparable threat to four level 27 characters. Meaning, characters that objectively don't exist and which are
at least +2 proficiency bonus beyond the upper limit of existing characters (and, at least in theory, another 1-2 feats/ASIs as well).
So like...we're already talking about going off the rails on things that were
inherently off-rails to begin with, given how sloppy and slapdash Challenge Rating has
always been as a mechanic. CR 20 is already dodgy
at best. There was never any hope that CR 27 would be any better.
But this gets into the thorny debate about stats and statblocks and what purpose they serve. I, personally, don't see the point of creating
clearly combat-focused statblocks for creatures that aren't actually meant to be
fought, but to be overcome in some other way that doesn't involve combat. Give them other descriptive numbers which are actually useful for how this creature is meant to affect the world and interact with the PCs. Trying to shoehorn that into the
combat-focused typical statistics of D&D is at best a pointless exercise, and in a likelier (and worse) case, distorting game design
and GM beliefs (and possibly player beliefs!) as a consequence of its existence.