Without disputing the discussion re: x-over and beaming which, in my view, is spot on, people might want to consider the other side of the coin.
If you cross from the mid driver to the tweeter much below 2K, you're nearing the a region where our hearing is more sensitive. Some would say that a well designed x-over circuit mated to appropriate drivers anywhere north of One-ish khz minimizes damage, but others disagree. The single driver crowd is all over this one.
I mentioned omnis earlier (and noted that they ARE rare) because they do satisfy both of these concerns. One driver is nearly full range (75hz to 7khz in my case) with only a subwoofer and (effictively) a supertweeter to augment. Dispersion remain essentially consistent without the need for x-over circuits where they MIGHT cause mischief.
Obviously, all designs involve trade-offs. This is just one more "recipe" to consider.
Marty