For these guys, basshorns or tons of reflex subs were always needed. It's all about the "bulk efficiency" issue you've discussed before. These days, power is available and inexpensive. And when they have to build up and tear down for each gig, size and portability become very important considerations.

But about "small basshorns" - I don't do them. If you go undersized, then response becomes peaky and EQ is required. They're direct radiators at the lowest frequencies anyway, so that sort of makes it a mute point. Midbass horns can be made small, but good quality hornsubs just can't be shoehorned into a small package.