Very old debate, in fact. Both design have been tested, and it somewhat seems that the current system is more appreciated/more balanced.

As far as i remember, there was a bit of "making BMs a bit more glamorous" while making the CMs a little bit less (ultra early CMs were too hard to counter)

Yes, there are often times when I never even utilize ballistic missiles just to get to cruise missiles.

Same thing can be said with the ships, have the all on one tree, or each by themselves.