With the middle-row seats slid back as far as possible, anyone sitting on them is treated to masses of leg room. True, if you slide them all the way forwards, taller adults will find their knees pressed against the front seatbacks, but you won't need to do this very often.
By contrast, the rearmost row in seven-seat versions is distinctly cramped. Leg room is particularly tight, and access isn't great either because the wheel arch juts into the space you have to squeeze through. The rearmost seats are fine for the occasional seven-up trip to rugby practice, though, and none of the Discovery Sport's premium-badged rivals even offer seven seats. If a usable seven-seater is a requirement of yours, look at the Kia Sorento, which has space for adults in its third row.
The seats in the third row fold away into the boot floor when they're not required, and are easy to lift up again one-handed.