Ya the issues with SS are pretty bad at the moment. Unfortunately, the fix for this issue is much more complicated due to how DoT's currently work in the game. Because DoT attacks have time lengths (18s etc.) that are unaffected by SS. Even if you allowed Spell Speed to affect the speed of DoT ticks (normally every 3 seconds) then you end up with a non linear stat gain path for SS on DoT classes.

For example:
18s DoT - Hits 6 times (every 3 seconds)
In order for the DoT to hit 7 times you would need 18/7 = 2.571 or 2.571/3 which is a massive 14.3% Spell Speed.

For a 24s DoT - you would need 11.1% Spell Speed to get an extra hit and so on for longer DoT's

Since the overall time does not change, spell speed for an 18s DoT attack sees no benefit until you reach individual marks, making the stat useless unless you reach certain milestones.