The 2 1/2 way is missing a high pass filter on what would normally be the midrange.
That’s the missing 1/2 component.
The advantages of 2 1/2 way speakers is usually having a small footprint but increased sensitivity, with some tradeoffs often occurring in the impedance being lower than it might be with a 3 way.
I’ve posted a thread here before that for many people the 2 1/2 way speaker may be ideal. Small, high output, deep bass.