1) Exp rate penalty gets less the bigger your entity becomes. The size of your
entity also reduces the exp-rate effects of spell 'rift scramble'.
2) The penalties when your entity dies have been reduced. You still lose sps
but not as much, and the amount you lose is reduced further if you have
completed "The Grind" task. Furthermore you no longer lose any exp.

I have added the following text to the guild book (page one - The Hunt):
Riftwalkers have long known that the experience gained when defeating their
foes is somewhat reduced by having summoned an entity into this world. Your
faithful minion will drain your own experience less as they grow in size and
power due in part by the hold of their own home world becoming less and less
as they experience more of this world, and share in the defeat of your
enemies.