There is currently a maximum attack speed of around 3 attacks per second imposed on the game.  This is likely in order to ensure that the game can run all script related to the damage dealt, and modifiers on the damage dealt, for all troops and heroes, even as the game gets complicated.  This causes a major balance issue, however, as anyone with a lot of bonuses to attack speed will find that a large amount of the bonus attack speed is going completely to waste, which is limiting the usefulness of other effects they may have that are based on their attack speed.

The hero who currently suffers the most from this is Kaylith.  With players easily obtaining 60-134% bonus attack speed from runes, 10-30% from swiftness set bonuses, 20-30% from air arena temple, and bonuses to attack speed from the elemental sanctum, players can easily end up with 100-150 attacks per minute, approaching the attack speed limit.  Now, Kaylith's ability which is supposed to increase her attack speed by 200% barely has any room to actually increase her attack speed.  This also reduces the effect of her artifacts, which are intended to benefit from the increased attack speed.  Any buff she receives from another hero while this ability is active is also no longer benefiting from being active during the increased attack speed.

It is very important that the coding for the game be made more efficient, or the engine improved, so that the game can afford to run attack speeds as high as the maximum obtainable attack speed in the game.  Right now, the maximum obtainable attack speed seems to be about  6-8 attacks per second for Kaylith, and about 3-4 attacks per second for some heroes such as Vara and Thalia.  Raising the limit is vital for balance in order for attack speed bonuses to remain effective.

To reduce lag and allow for the game to properly calculate more attacks per second (and the modifiers of damage and bonus on-hit damages dealt on each attack), a system with different damage text options would be vital: One that uses the current system, showing all individual pieces of damage dealt to each unit, one that combines all damage dealt on an immediate hit to one text value (for example, a shadow infiltrator flank attacking and dealing his ability's extra hit, while proccing aldeus's on-hit damage and encaria's on-hit damage, would have the total of all of his damage dealt to the target at that instant displayed as one value, the total of the amount of damage dealt to the target in that instant.  This would reduce lag, and be known as the "Combined Damage" text option.  Another option would be the "Per Second" damage text, which would display the total of all damage dealt to a target each second, above the target hit, further reducing the amount of text that must be rendered and reducing the resource footprint of running combat script.  And, finally, players would have the option to disable combat text entirely, to reduce lag as much as possible.  These changes, combined with improvements to code, might allow for a higher maximum attack speed.

In the meantime, here is my proposed temporary solution to Kaylith's ability, so that it can at least get some utilization without wasting the extra attack speed:

Level 1: +80% Attack speed for 8 seconds.
Level 2: Duration increased to 10 seconds.
Level 3: Duration increased to 12 seconds.
Level 4: Also gain 15% Attack Power for the duration.
Level 5: Duration increased to 14 seconds.
Level 6: Also gain 30% Attack Power for the duration.
Level 7: Duration increased to 16 seconds and gain 35% Attack Power for the duration.

This would serve to keep her ability useful; you could change it back to the original +200% bonus attack speed for 8 seconds once you get the other limiting factors in the game fixed.