It seems that it would add a layer of protection from possible hostile entities. We protect the chain from possible incoming hostile entities by making them wait one month to fully participate.
It would affect a lot of the smaller accounts, but the reality is that only the large accounts vote the witness in vote for proposals and other such things. The ability for the small accounts to effect who is is not a top 20 witness is pretty insignificant.
But yes having a smaller group of people controlling things would be just as bad, however the small accounts would then have more power to determine who is and who is not a top 20 witness.