The quantize button on decks is now a switch both for rounding (hot)cues and loops to beats as well as compensating for the user pressing the play button off beat. These are distinct use cases and IMO should be separated like they are in Traktor. I almost always want cues and loops snapped to beats, but I often do not want the play button correction when playing a track that has an incorrect beatgrid and/or starting a track without beatmatching. Traktor has separate Snap and Quantize buttons. Snap covers rounding (hot)cues and loops to beats and Quantize handles manipulation of playback. I want to use these options at different times and not always together. It gets confusing to toggle the state of the Quantize button when I want one behavior but not the other.
Also, I do not think each deck should have its own Quantize and Snap button. It's easy to forget which deck is in what state. If there were only global buttons, it would be easier for me to know with certainty what will happen when I press other buttons without having to look at my screen first.
Just making a comment as I found your wording here so clarifying for others how these work in Traktor.
"Traktor has separate Snap and Quantize buttons. Snap covers rounding (hot)cues and loops to beats and Quantize handles manipulation of playback."
Snap is for the settings of cue and loop points but doesn't affect playback in any way. Quantise is for playback, including keeping the triggering of hutcues or loops in time on the beat.
I've never found it an issue these being one and the same in Mixxx. Quantise is definitely useful to have separate for each deck though, especially if the music you are mixing is hard quantised/perfectly beatgrided mixed in with tracks where the tempo fluctuates and the grid is a only approximate.