Do the young really want TV for them?
When it was being launched, JSP said that it wasn't going to do everything because young people already watched drama like Neighbours and alternative comedy, but they generally didn't watch factual programmes so they needed to be made in a different way, and that was what DEF II was going to concentrate on, with things like Reportage and Rough Guides. Similarly there was never one catch-all DEF II music show but shows that covered different genres.
I became a teenager while DEF II was on and I can't say I watched it all the time, but by its very nature you weren't going to watch all of it, and it was quite patchy as well, it never had the budgets or scheduling to commission new stuff all year round so it relied on a lot of repeats and recycled stuff from CBBC (like Degrassi Junior High, including some episodes that were considered too adult for CBBC) and schools programmes and the regions and primetime (like repeats of the Real McCoy). If they'd put more money into it, it would have had a bit more swagger.
The DEF II show I always watched was Dance Energy, because I was into all that at the time, and I particularly enjoyed it when it became Dance Energy House Party, with the show relocating to Normski's "house", ie a blatantly obvious studio set. They really broadened the music policy and put a load of indie dance crossover on and also added comedy, and it was highly entertaining. Used to watch the Fresh Prince at the time too. You knew what the point of DEF II was and I think it did a better job than most at attracting young people, certainly it had an impact on what C4 were doing, they started showing youth-skewing programmes in the 6-7pm hour.
Of course though DEF II was on Mondays and Wednesdays, on Wednesdays it didn't actually start until 6.50 and Star Trek The Next Generation, and then the original Star Trek when TNG was exclusive to Sky for a few years, went out at six as a proper BBC2 programme. At the time apparently there was also a memo going around the Beeb that TNG had to start exactly on time because if it was even a minute late they'd get a thousand complaints from Trekkies.
One odd thing is that during much of the run of DEF II, Friday nights had equally young-skewing programming, all the ITC repeats were there, plus Doctor Who and in January 1992, the show 100% which was supposed to be a halfway house between CBBC and DEF II, starring Trevor and Simon, which was actually a CBBC production (and which was going to get a second series but which was axed right at the last minute as there was an accounting cockup and the Beeb had gone massively over-budget and axed a load of shows to save money). The Living Soap was in that Friday slot too, in 1993. But for some reason that was never billed as DEF II even though the line-up certainly wouldn't have seemed out of place.