It my be too early to tell, but As far as Alexander's being tied to our 2hr ability, it may be justified - depending on the defense, number of status ailments it blocks, and duration.
Odin's, on the other hand....I dunno. If all it does is automatically kill things - and only damages HNMs - and its hampered if there are multiple enemies - that sounds as if its just not worth it as a two hour. The only real place that could be useful is in places like dynamis - but if there is a chance it can miss (and it seems like it will be high for multiple mobs) this just isnt worth it. And if his damage on HNMs is compairable to all of the other avatar's damage...there is no point to him being a 2hr only avatar.
I guess we will have to wait and see.