Mirror's Edge has six-to-eight hours of pure content right from the get go, each level is drastically different from the last and fairly HUGE. Then they use the time trials on top of that. So its foundation is immensely larger than Steel Diver, which reuses far fewer assets over and over and over and over and over again in slight, infinitesimally different ways.
They're similar in that they both have time trial modes. They're not similar in terms of how much pure content they have.
Steel Diver's main missions are all unlocked easily without a sweat in 2-to-3 hours. The amount of pure content in this case is very light, almost offensively so. Actually I'd say
explicitly offensively so, since nearly all reviewers and a large chunk of user reviews are similarly put off by it.
Side Note: And even with MIRROR'S EDGE, some reviewers thought it was too light on content. So we're talking degrees here.
Effect said:
If each of the subs control differently (which they do) I think it does count. How you approach the level (even though you know it's layout) has to be different depending on which sub you are using. The play experience is actually different.
So a racing game has a billion hours of content because, after all, you're not really playing it unless you play every track with every individual car. After all, all vehicles control and handle slightly differently!
P.S. Nobody sane would make this argument
Also, the subs are not even as drastically different as vehicles tend to be in racing games. They do NOT change the way the game feels much at all. It's not even a Pilotwings difference.