Imo speaker design is always system design, wherein the room and even the amplifier are parts of the system.
I've done two-way speakers that have good in-room response from the mid-20's up to 18 kHz or so, but these were not polite little mini-monitors. They were big floorstanders that used components designed for recording studios, which could deliver 115 dB peaks anywhere in their passband with less than 1 dB of thermal compression.
Why use a two-way in a size and price range that left plenty of room for going three- or four-way? Because a pair of high-quality large diameter midwoofers kill three birds with one stone: They move enough air down low; they are directional enough up high (for good pattern-matching with a constant-directivity waveguide-style horn); and they have the efficiency, impedance, and thermal power handling that I wanted. This adds up to good synergy with the room and with the amplifier types I had in mind,
I have since come to embrace more complex approaches for some applications, but the core element is still a high output, controlled-pattern two-way.
Duke