I don't know to whom this was aimed. So I won't answer everything.
How's your economy structured? I hate to criticize the articles written about cultural victories but they tend to go Cottage economy for the most part. Have you tried setting up an early GP farm and aiming for those great artists? You could probably cut down the victory time by a few turns by either settling them as residents or saving them towards the end for that last quick culture boost.
Are you aware of the number of great people you need to get a city to legendary ?(on quick it's a lot less, that's why this setting is better)
Let's pick normal speed (my usual setting) :
50.000 culture needed, in 3 cities
Each GP brings 4000 culture.
That's 13 GA needed.
Let's hope you have a few culture building, even without using the slider.
If you do this very carefully you could be down to 10 artists needed per city.
1 or 2 less for the capital.
28 artists is a lot.
How do you plan to get that many artists in time?
When you're very dedicated, you manage to have 6 to 10 artists waiting to do there job. Quite far away...
Sure, you can use research and expand longer, and thus gain a few more.
But they are getting costly with the numbers, you know.
And large expansion I would consider a necessary evil. It hurts with the upkeep but if you focus with those three cities on culture I believe you can maintain a decent army and if you're pulling enough gold (I usually cottage spam, w/ exception to the GP farm, like hell anyways) you can still stay in the game with a 10% research rate. Of course if you pull it off just right you probably wouldn't need the army nor the research at that point.
what's your point?
expansion is good.
Achieving cultural victory with 15 cities is easier than with 6.
Not faster though.
I can't say I've been playing the cultural angle much these days (I did when I first started out, they were my first victs; I was getting there around 1850+ Noble/Normal). But taking down an opposing civ early did help as mentioned before. I think the best determinate would be starting position, a first city next to two gold mines certainly will give you a great lead in researching some early religions and pyramids (if you go that route)
For every victory condition, a multi gold city is good.
Of course I find the cultural harder since I lost my Vanilla Catherine's Financial trait to Warlords (although Imperialistic isn't that bad). Maybe I should go back to vanilla to see what I can pull off now...
try another leader!
In warlords, Huyna Capac or Mansa Musa are great for cultural.
My favourite in vanilla or warlords is still Isabella.