Ok, let's go!
First, I would like to reiterate that I don't think writing takes as much time as art in the great majority of the cases. The main reason I discussed exceptions is that it's one of the reasons I see for people to get upset when we discuss how profit can't be split 50/50: they can always give a few exceptions or unfair cases and focus on them like if it was the rule; what I meant to say was, yes, there may be exceptions, but there are only that: exceptions, to a general rule that should be considered FIRST.
Anyway, for my example (another disclamer, haha. I'm absolutely not a professional comic artist and that project I'm going to speak of would have had 0 chances of a commercial success – you'll see 
- So this is a very theoretical case of 'writing would take as long/longer than drawing).
So, that was my first project, before the comic I'm currently drawing.
I gave up because of the insanely demanding writing process.
This was a short (~40 pages) story with a simple plot. A young Sumerian prince is enjoying jams made from fruits from his own orchard since he was a little boy. As a young adult, he end up meeting the family of farmers/servants who were making these jams all this time. These are pretty alien worlds meeting, the only link between them being this never ending flow of fruit jam. Reflexion on the social structure of the society, and questioning ensues.
Now, the idea was to tell this story as a European Middle Age tale that slowly came its way from Sumer times through various manuscripts from the Arab world.
I worked on it enough to realize I could do something pertinent with it, but that it would take an horrible amount of time:
Find enough info about Sumer society structure, and enough about the social norms etc to write believable characters; plug the numerous holes in a pertinent way (there is not THAT much info available, a lot of educated guessing needs to be done, and to do the educated guessing you need to be.. educated). Fighting to find the adequate sources, there are a lot of works and text translations that have not been republished in the last 50 years, and not everything is scanned yet. Generally, it's very difficult to find the right sources even when they exist.
Then, decide a way for the story to reach MA Europe. It does not need to be precise, but still: this is very important because it will determine how altered the story will be by the successive cultures that translated or even adapted them.
Decide how the story will be adapted to fit these new cultures (of the translator/adaptor). Depending on what steps were chosen for the story's version history, one now need to redo all the research about social structure, norms etc, and adapt the story accordingly.
This is AN ENORMOUS amount of work for 40 pages! And that's why I gave up.
On the other side, the drawing part is not that bad. The drawing style can be lifted from existing manuscripts, and I had an idea from the beginning of the project; but I'd need a few hours to go through the historical material found during the writing process to avoid inconsistencies.. let's say 300 hours drawing (probably less)... Well, I'm absolutely certain I can't do all the research in less than 300h.
So yeah, for me, that's a project where the drawing side is the simplest and probably takes about the same time as the research/writing.
BUT! It's a crazy, unsellable project that makes sense only as a self-financed, vanity project.
If I ever have the money, though, I already know a few persons that I would trust with the project, and would gladly pay for whatever hours they need, if they'd like to do it.
