Thanks for your feedback!
nice catch! there is indeed a very short cooldown for fireballs. The idea behind it was to avoid excessive spam of fireballs, which would have been detrimental both gameplay-wise (e.g. you could spam while walking) and performance-wise (I haven't really had time to optimize the code and I'm instantiating and destroying them each time).
Regarding the implementation of a visual indicator for the cooldown, I usually agree that it is a very nice feature but I feel it would be kind of awkward with such a short delay: the player would just catch a glimpse of it. It would surely be registered, but I'm not sure it would be consciously perceived and correctly interpreted by the player, rather than being perceived as noise or distracting. If you already have implemented it for short delays in past games, I'd really like to know what was the feedback on this regard.
Cheers and thanks again for your input!