I don't think the missing reward go to other miners, it goes to the owner.
Not true, because 'the block reward + fees - poll fee' is divided based on each miners score compared to the total score. The only reward that Slush gets is the pool fee.
Which also makes Slush useless for backup pool
This is true. Slush aims at full time miners using other pools as backups, not the opposite.
Outright theft and most people are ok with that. I want that kind of blind loyalty.
Theft - No.
Loyalty - Yes
Blind - No. Slush have proved to be scrupulous in the last 2+ years (since I am mining here). A bit slower in fixing things lately, but always fixing them right.