I’m not sure whether this is necessarily true; if a hyper above 235ft in height (I know RCDB says Big One is 213ft, but the park claims 235ft, so it would probably be best to aim for that figure) were to be built, it would become the UK’s tallest roller coaster, and possibly fastest as well dependent on how high it was built; a hyper with a drop of above about 230ft or so would likely exceed Stealth’s 80mph. A hyper of this size would also be in with a fair shot at claiming the UK length record (it’s technically now held by the Big One at 5,497ft, as the Ultimate is SBNO).
Even though a ride like this wouldn’t have a world’s first per se, I think that “the tallest & fastest coaster in the UK”, or even “the tallest, fastest and longest coaster in the UK” if they fancied beating the Big One’s length record, would be incredibly marketable and would make a big splash within the UK industry; look at the likes of Smiler, Big One, the Ultimate, even Thorpe’s own Colossus, Stealth and Saw. These rides all had either national or worldwide records at the time of opening, and they were all incredibly popular. Rightly or wrongly, I think records sell in Britain, and based on the likes of Smiler (no real world’s first besides the record), I’d argue that a UK record breaker would be a pretty compelling sell to Merlin.
In terms of whether the lack of inversions would make it seem tame; the likes of Big One and Stealth have certainly coped fine in terms of public opinion and reputation even without inversions, so I’m confident that a Thorpe hyper would be the same, personally.
A hyper may not have a gimmick in the traditional Merlin sense, but I think it would be equally as marketable!