Doubtful. You have to deal with the OS and it's API layers which can be bypassed on the Vita, plus, out of the thousands of games for iOS,
There is one problem with that. It does in general not apply for the first generation games. The reason why Consoles ( fixed or handheld ), can last "longer", is because over time, developers, learn the in-and-out of the consoles, and it allows them like you said, to bypass the API layer.
But! In general, the first generation of games, is mostly written on the API layer. That is also why you see a difference between first generation games, and later generation.
Technically, there is no reason for the iPad, assuming its running a Quad Core / SGX543MP4, to not come close to that type of first generation graphics.
Of course there are other factors also. Sony there Vita is running a special SGX543MP4+, with 128MB dedicated memory ( probably faster memory ).
On the other hand, do not forget, the Sony Vita is build on 40nm process.
If, and its speculation, if the A6 is build on 32 or 28nm, there is a change that the CPU/GPU can be higher clocked then the default of the Vita. This can offset some of the disadvantage running on the API layer.
Think nobody even knows what the Vita is running at right now. And technically, it only uses 3 cores for its games. The 4th core is reserved for the OS.
I feel only two companies, chair (Infinity Blade series) and Firemint (Real Racing) actually try to take full advantage of the GPU. Most developers instead target the Angry Birds crowd since it's a lot easier to make money on cheaper 2D games than 3D ones.
Reason for that is simply put: Lack of game development support, and lack of controls. Especially that last part really hurts any tablet in regards to turning into a "Gaming Console Tablet".
One thing i have been wondering about is, that in reality there is nothing stopping a game developer from going beyond the API layer, as all the iPad's are based on the same architecture ( A4, A5, A6, they are all ARM based, with the same GPU design each time ). Just Apple being troublesome
We shall see. Think to be honest, that if Apple had some physical control's, and
game developers support, that a LOT of game development companies ( the big one's ) will jump on the iPad as a gaming device.