You don't need mix to do decompression dives, you MAY need mix to go deeper. Doing a 70 minute dive at 100ft is a decompression dive, on 32 and O2 it is very doable.
I think too much is focussed on 'mix' rather than doing a decompression dive correctly. While mix has its benefits, we should not equate having mix as equaling of doing a good deco dive.
I don't see a single person here stating otherwise. I myself do a fair amount of non-mix deco diving well within recreational depth ranges. (Which is pretty tough at times to do as the cold gets us first sometimes).
Using mix is primarily a function of depth, and deco classes these days are being promoted to depths (on air) deeper than their same mix classes run their END's with.
Sounds rather tenuous to me.