Imho (and mho rocks

-the link breaks too easily once established
the problem with the DoT ones is:
-it deals, overall, less damage than chain-casting a regular spell, or casting double missiles
-it is quite hard to get a link: I take it you won't use DoT spells to solo, but rather when in a team. And when you're teamed, you often have to hit mobs that are way above your level to get any decent xp.
-even when you get one, the link breaks too easily
Does anyone here use the Direct Damage + DoT double spell stanza ?
I don't.
I think the link-type spells definitely need a boost, a big boost.
While i'm at it, lemme highlight what I consider and have ticket'd as a bug, even though I might be wrong, it could be an hidden feature

When you cast a link spell, no matter how you paid for its cost (your own hp, range, time...) when the link is established, it will only drain your sap.