You are both correct. The arrangement of the spells makes different forms of access easier or harder. It just depends on what your information need is.
Putting them in groups by class and level as 1e/2e did makes accessing them easier for players making their spell choices when preparing their spells. This, however, can also lead to repetition as spells are shared by multiple class lists so you either have to repeat the whole description or have a reference for the user to flip to some other class's list for the description (also seen in 1e/2e).
Putting them into an alphabetical list makes accessing them easier if you're looking them up during play when a spell of any class could come zipping by. You also avoid repetition or having to use lookup references described above.
There are good arguments for going either way. But WotC has favored the second approach for 3e and 5e.