I didn't say that it must be a big exchange at the beginning. If it's a good project it could also boost on etherdelta.
ED is ok for 2 days, SOMA must have a partnership with an exchange for after there ICO.
A fast listed project right after ICO will give you investors who were just to late, if it takes to long those investors will be to another project or forgot about it. Exchanges are very important and I dont think ED is that one.
The problem with Etherdela is, that most people just don't like to trade on it so a different exchange would be nice. But I also think, it doesn't need to be Bittrex or Polo to become successful.