The impedance of the speaker can easily make a difference. In some cases can change the class of operation too (lower impedance pushes the amps more towards the B region; yet another reason to avoid low impedance speakers if possible).
That makes a lot of sense.
Class D amps are a better solution than Class a/b then perhaps in case of harder load speakers. A good one seems to operate much more optimally and consistently even with lower impedance/efficiency speakers.
Class A to do the job especially if speakers are less efficienct could be very large expensive and power hungry so not a practical option for many.
I often think if not for teh success I have experienced with good Class D amps, I would likely be more in the tube amp/easy load speaker camp by now. I’m glad I decided to try that first. I found it hard to find a Class A/B amp to do the job and sound as good as a good tube amp setup (with right matching speakers), but not the case with good Class D amps and most any good quality speaker out there today although finding the right sounding match there for each individual is still teh key to highest level of satisfaction.