Yes I considered that and also tried with the Focusrite; please note that I do need an external audio device for some serious output (2x TS jack) to feed my PA especially when doing live gigs. So using the built-in audio-output of the iPad isn't good enough.
But the point is that also at a gig you want to have as less equipment as possible, so the SL was a dream setup. Just plugging in the iPad and you're good to go. Like their website says "professional grade audio interface" one would expect also to have a good setup for live gigs. But maybe it was just related to the quality, not to playability :-) And then...the Focusrite is still better in clarity and performance.
As fas as your suggestion concerns, just using it as a controller not as audio isn't that bad but that's not how it should be. Not in my case anyway.