Well, I have noticed the same - using the spirits not always gives XP.
Still I believe that even if I don't kill an enemy I should get something for using rage skill.
Maybe even shield or wall of stone gives XP - but the shield first when it is attacked and wall when it is destroyed (also the icy dots of rage and mana - if they are consumed - they could give XP to Lina, if not then not...)
But not getting any XP at all for using defensive spirit abilities is not fair at all. (But at least the undead Guardian guy will always have fast leveling and for me is still the most usefull one
)