I would not agree with that: if ice is your secondary any spell should work for you in exactly the same way as it works for an ice mage of same lvl with same equip, just as defense skills raise the res of warriors even though they dont have that tree as their main and just as rogues use lupine succesfully even though they are not explorers.
Its not easy having 45 in ice as secondary, especially at higher lvls. Priests also have powerful spells at lvl 45 (can't remember the other 2 classes, but I think its different lvls): following that thinking a buffer healer should not have access to such a powerful heal as 1920 and a healer duffer should not have access to such a powerful duff as parasite. [/b]
the lower the lvl of skill is, lower slow success rate should be. lvl 45 skill should have low success rate to high lvl characters.
lvl 70+ ice skill should have high slow rate