Agreed. Interim titles are nothing more than marketing schemes. They don't progress the division at all while the champ is gone. It is just as held up as even the interim champ knows he is still only the #1 contender and not the real champ.
Well I don't think their is anything wrong with marketing better for a big title fight than a month of being sold on TJ Dillashaw.
But look at the history
Arlovski/Sylvia - Launched a championship trilogy
Sylvia/Nog - Got Nog a title which has kept him at the top of the card ever since...CC didn't have that.
Mir/Nog - setup the greatest show in UFC history
Carwin/Mir - Co-Main evented the absurd Hardy/GSP mismatch(which is why we need the WW one)
Couture/Liddell - Launched another championship trilogy. ended the Tito era
GSP/Hughes - main evented a fantastic card started the run for the UFC's biggest draw of the post Lesnar era
Condit/Diaz - did 400K buys and set up co-main eventers for years to come.
Barao/Faber - current champion and set up a huge rematch
So of the 8 interim title fights only one(Carwin/Mir) you could argue didn't have a lasting and profound impact on the sport.