I have always had Join in Progress checked since I unlocked Duty Finder (I queue Tank and I like helping stranded groups) and I always Solo queue. All of my issues with huge queue times were not improved or affected by those habits (or at least, definitely not enough to be a "/thread"-worthy solution).
I will make note of checking Join in Progress though — that's a good point I missed, because every little bit helps.
I'm not sure. It's one of those community folk wisdoms that I've seen repeated so many times that it begins to get taken at face value. That said, I have also seen many (admittedly ancedotal) posts around the FFXIV communities where players solved their impossibly long queue by checking the majority language and unchecking the minorities — I know that's not the experimental data you're looking for, though.
