Actually, you are wrong on both counts.
The 787b was a sleeper, because it was slow as all hell compared to the other cars in the race that year (mostly due to it's rev limiter and lack of torque). And the 787b wasn't banned from Le Mans (though you were much closer than your other point), but Wankel rotary engines in general were banned (pointlessly) in all FIA races for fear it would permutate into F1 or something. Which is why the FD RX-7 never really had international racing success.
Every single other Group C car (well, maybe not the Minolta, ironically enough) should be faster than the 787b. The only one that is really definitively slower is the Peugoet 905, which is odd as it should probably be close to the fastest car in the game, if only due to it's handling prowess.