The spell was capable of lasting, what, FIFTY seconds before, if you had it at tier 5? Nobody ever complained about it during earlier versions.
To be honest, I've complained about it when it first was introduced, and wrote the Mantis issue sometime in April. I never brought it up in the forums until this recent change to increase the default duration. So, yes, 50 seconds is worthy of all caps and sounding ridiculous and whatnot.
And really, the complaints don't make sense to me.
My complaints are about the whole darkness system. Darkness is an obstacle, like water, or terrain, or monsters.
Acid water requires sacrifice to deal with. You need to use an enchant or pick a Skelebot to avoid it. Both of these come with giving up some maneuverability and even defensive capabilities. A spell that just let your breath water for 30 seconds would trivialize it.
Terrain requires jumping and placing platforms. There is "transmogrify into bat" as a limited use scroll, but it hurts your damage output and increases your incoming damage. If this was replaced by a 30 second duration fly spell that only cost mana, it would trivialize terrain.
Monsters require fighting and dodging. (This example is rather extreme, but I hope you see my point.
) A spell that just froze every monster in a chunk for 30 seconds, that just cost mana and had no cooldown, would just remove the obstacle entirely.
This brings be to darkness.First, what is darkness trying to accomplish as an obstacle?
I believe it serves many purposes. It gives caves a different feel from the outdoors or even inside buildings. It hides monsters from the player. It makes platform jumping more difficult. These are all bad things that the player wants to avoid. There is no give and take with darkness, no benefit for leaving it.
Next, what are the players options for dealing with darkness?
As you mentioned, it can be completely ignored for picking a Drakonite. They are very slow and require a different enchant load-out make up for their deficiencies. There are various strength emit light enchants that can fit on at least two different slots, which can mitigate some darkness at the expense of other bonuses.
A whole host of spells can be used to provide light in various different ways. Permanent stationary, long range temporary, dropping lamps, crawling snakes. These all have pros and cons and come with varying resource and opportunity costs.
All these different methods for dealing with the affects of darkness are what the obstacle is balanced around. Flash of Light is the "gimme" option. It is not a meaningful game play choice. Casting it is busy work. No thought, just remembering to cast it every 20 seconds so it doesn't run out. Personally, I find that more annoying than compelling.
I would suggest a difficulty toggle of "no darkness" instead. For people who can't be bothered with the other options, or are so annoyed by darkness it has a great negative impact on their enjoyment, just get rid of it.