Disagree. All things considered, Thorpe's coasters deliver a great thrill for their length. More importantly, I don't think the likes of Colossus, Inferno and Saw would be improved with a longer length. Stealth is designed to be a short and sweet ride, and with its restraints, I don't think a particularly longer ride would add much. The only major coaster that would benefit from being longer is Swarm, but even then, I don't think it's *that* much of an issue.
Also, fun fact: Smiler aside, the major coasters at Towers are, on average, the same length as Thorpe's. And their length is rarely complained.
I don't think Thorpe lacks a headliner - Stealth fits that role perfectly. The trouble is when we look at big parks across the world which have added major attractions over the past 5 years or so, they've added in fantastic new investments which make use of technology which simply wasn't available 10 years ago. And then these new rides just naturally fit the bill of being a new headliner.
So it's not that Thorpe lacks a headliner - for the majority of people who don't know what's out there, they'll still Stealth as a major draw. But when you follow the industry or know it further, you realise that because of the lack of investment for the past few years, the park simply hasn't kept up with modern trends like major parks have.