Just make a refrigerator sized cabinet and you’ll get your combination of efficiency and extension, or put a sub at the right spot (which would execute better)...that’s not the point....Modern high end PA has attributes that old altecs didn’t quite get to...holographia, slam, whatever for days..watch some big meyer bluehorn disappear like a piece of cake and let me know when the altec did something close....
On the other hand horn design has progressed considerably, and compression driver design has progressed, and some modern prosound or prosound-style woofers outperform the Altec woofers in areas other than their combination of efficiency and low-end extension.