No, better in any aspect definitely not. They are differrent and perform differently, better or worst, according the situation. And in lot of cases, they perfom both very well.
First of all, there aren’t neither the necro an thed demo, but the necroS and the demoS cause build can change, even a lot, performances and way to fight, even when the differences can seem subtile (not all hybrid demo builds are the same). I play a no-pet (mainly nightfall) necro (rarely I switch to a pet build) and an hybrid demo (now, always the same build) relying on instant casts, wave of flame AA, a lot of CC, but even max range shockstrike.
In terms of max dps (total, highest shot and critical), expecially in spellweaving when u can do a sustained damage, yes, necro usually outperform a demo in an encounter. Then the necro can apply a greater number of weaknesses/damage over time (dot, ruins, etc) than a demo and can do mana drain.
From the other side, even if necro can have instant spells, his spells are usually slower and a demo can deliver very very fast a lot of damage in few seconds (with shock and hellfire stream instant, wave of flame + ring of fire for example), can hit and hit hard while running (his instant perform very well), has even more fast and reliable CC on single target (storm chain and fiery torment are fast and last enough) even if necro has a great arsenal of group CC (but slow to apply, except frost blast).
Talking about demo CC, then, detonation is a great group kb/damage spell, is far better than thunderclap and (if u have hellfire stream as instant) is even the fastest single-minion oneshot-spell you can have in a raid group.
Both classes kite very well if you are a good kiter, ofcourse, because one could even have the best build and gear, but skills come first.
At the end, in group/raid, in my opinion they perform both very well, even if a necro can provide a more solid dps.
In solo, in wild, well this is a matter of tastes, they are both strong, but a necro, even if well played, will never reach a demo as elegance fighting a crowd of mobs all togheter cause demo is essentially a fast fighter relying on burst damage, cc, speed and being always in movement. In this way, the class more similar, as feeling, is the assassin and both classes fight in a spectacular way.