The problem with bands like that is that there are thousands of them and only very few actually make it big.
For example, a band like Eu*Phoria failed despite Avex's back-up. Some members ended up in Gacharic Spin, which also had band members from three or four other 'failed' girl rock groups. Gachapin is now transforming into Doll$boxx, etc, etc. The point being that even with top musicians and proper back-up it's still difficult to make it. Scandal is one of the few newer bands who are still successful after a number of years.
The fact that they had Sayaka as a member doesn't mean anything since she completely unknown at the time. Actually, there is a perfect precedent to Mad Catz. Oshima Yuko was a band called Doll's Vox, produced by The Alfee's Takamizawa Toshihiko (!!!). it doesn't get much better than that but even they failed miserably
So yeah, as far as Sayaka is concerned, she is waaay better of being in NMB48 (the captain and shared center at that).
edit:
As far as the "write ten songs" deal is concerned, that isn't such a surprising thing to come from a record company. For example, Gus G had to write like 20 songs in a very short time to get his band Firewind of the ground. They test what the artist can do and can check if there is enough material to work with for a single/album release.