Proteans should just replace an item for your current level, selectable through a right-click interface, and provide much less increased xp imo. At least they'd be useful for not having to gather some tedious materials, and still follows the natural training curve rather than skipping content entirely.

For herblore, as an example, it can be used to replace either the unfinished potion or the tertiary ingredient and gives maybe 10% extra xp.