The bottom line of your goal. Don't sugar coat it.
Nor is this a just 'slight increase' you speak of
OK... but then
the exact same shit the other way around
I feel this was the only question and the rest is just some self-righteous rant no different from the bible preachers coming on campus telling everyone that they are going to hell.
I can't really tell you the exact time as most of my achievements dates are overwritten by my last server transfer in March 2014. So you can either take my word for it or whatever but my characters are fresh ARR characters.
I started 2nd week of September 2013 after trying and failing to get on my first choice server Mandragora due to server locking which I transferred to it during the first week of December 2013.
During this time, which was less than 3 months - I capped all DoH/DoL/DoW/DoM - this is before dungeon exp increase, before beastmen tribes, possibly before roulettes too(?), and before leve exp adjustments (you get less exp from DoH and DoL leves before but for DoH leves, you get a 200% bonus instead of the 100% now)
My alt I started after my 2nd transfer to Balmung - I did not spend that much time on it, leveled DoH/DoL almost purely off GC daily turn ins. So yes it took several months but also close to no effort as it was extremely easy to obtain all HQ from my main char.
TL;DR
It works fine the way it is now.
If it ain't broke, don't fix it.