So he has a design philosophy, it doesn't mean he's correct. For a fullish range speaker, say 40Hz up, I can make very good argument for 3 or more way for hifi, bass guitar* or PA.My friend has been designing speakers, for HiFi, PA and MI LFSys. He is fastidious about the design of crossovers and does not use 3 way designs. He does use 10,12 and 15” woofers and compression driver/horns capable of going down below, the beaming region of the woofer. To get the correct response you must match/use the horn and comp driver, not necessarily from the same brand.
I use one of his designs, the Silverstone, an FRFR passive design that outclasses most HiFi speakers.
* My last large BG rig was 3 way, and was dismantled for my recent house move and is due to be rebuilt soon. It will also be 3 way and FRFR, but I've been using this sort of cab for over 20y. I pretty much only play 6s these days, B-C and E-F.
In honesty, I did a local party gig just before Christmas and used my old Peavey Mk IV/BW15 rig as it was to hand. It worked but was muddy. As the dance floor was full all night, I'm sure I'm the only one who noticed or cared.