Does music key still matter regarding guitar?

Yes it still does.

I'm not quite sure of what you mean. Key matters whatever instrument is being played, especially if you are playing with other people.

If you mean is it necessary to tune the guitar according to what key the music is in, no, but nowadays that's true of all instruments.

I think you probably mean that all notes are equally dissonant, rather than “distant”.

Of course it does!

If you are playing as part of a band/group, what you play and what they play has to work together to form the overall piece of music, a harmony rather than a discord.

All using the same key as a basis allows that to happen

Keyboard instruments and synthesisers etc. are also generally "equal temperament" - playing in key is a very different thing.

If you are playing solo then do what you like, but if you are part of a team, alongside other people, you need coordination between the members of the team for it to work well.