Those cards you mentioned really are not OP on their own. If all cards would be allowed, Ongh would have to be backed up by Slyth cr to stand a chance against the other OP cards that would room about. Skeelz as a whole can't really do anything without Caelus Cr. Uppers are not perfect without Jackie Cr. Robb Cr needs support from Marina and Lamar Cr for All-stars to have a chance in this 'Elo FFA'. This kind of thing goes for most of the powerful clans: You need an extremely expensive card, which are collectors more often then not, to even have a decent fighting chance. And that's not even mentioning how expensive other staples could be, like Zatman, Gil and Ongh.
All fine and dandy if you're rich and/or a veteran, but most of us ain't that.