Low intel monsters with High CR are meant to be beaten with guess what intelligence, so i really do not understand the issue, if figured out ligimitally in game, with it being beaten as described.
yup some of my favorite stories are ones where a PC hit WAY out of his league and killed something with a smart move... my problem is it isn't "intelligence" it's "Use a very basic strategy"
I don't think there is anything metagaming about it... IF I made a complete refluff of the monster, but it was still animal intellect, had no ranged attack, and was a supposed to be a threat in the open, then my party would most likely still pepper it with ranged attacks...if not to kill it (although they might) at least to weaken it.
I'm not even talking about a 5th level wizard spaming a cantrip... I mean a full on hit hard with lots of stuff but from X feet away where X is greater then it's move+ reach and/or throw distance....
Also your point about having to design a how encounter around it, are you for real? Its literally a mythological creature of legend and the second or highest CR in the whole of 5th edition, if your telling me it doesnt deserve a moments thought and effort to make it pretty epic then remind me to not show up at your table any time soon. (tongue and cheek intended opposed to genuine insult)
It does require some thought... and the fact that it requires more to counter a massive whole is annoying...especially when said whole was smaller or non issue in other editions.
past uses in my game of Big T
2e, I had one wake up in the middle of my party (at the time just having hit 17th level) sleeping in an inn, and it attacked the city (1st time I ever used)
2e, I had a BBEG force port them to flax... then ran no less then 7 encounters... only 1 of witch was a full fight instead of trying to outsmart/get away.
3.0, party just hit 5th level I had one wake up in the far south and rampage through mostly empty woods falling back to sleep within sight of the southern boarder of the kingdom the PCs knew... The PCs where shortly there after told that in 14 months it would wake up for it's longest rampage yet, and destroy the kingdom. This was added to 3 other things going on at same time.
3.0 same party at level 14 had to fight and slay that tarrasque but with the yearish to prep first.
3.0 in a game where the PCs where all demi humans (divine rank 0) I used them when ever one of the big gods got pissed... I think the party fought 4 or 5 over a 10 level spread from level 5-15.
3.5 had one sleeping in a kobold cave that my party had to clean out to claim some land... it wasn't due to wake up for over a decade. (Kobolds worshiped the sleeping dragon god)
3.5 used stats scaled down to medium for my "Armageddon Beast" that used my Doomsday mini
4e had a 1 off game with 9 players where they hunted and killed it at gen con
homebrew mish mash system had one slain and pieces pulled off and magicaly bound to soldiers making them unkillable.(with out a wish spell) then invaded the PCs country...
wow... so 9 times over almost 20 years... I guess I have used it a lot.