In most cases, they are not. If you play Leona or BCBlitzcrank, you basicly WANT to get early kills, cause else the enemy support will outscale you anyways. So if you take gp10 seals, it throws you behind in laning phase, while laning phase is your only strenth and you should try to get an advantage.
On Leona and Blitzcrank, I wouldn't ever take gp10 seals (Armor instead), cause you only win if you are able to play aggressive. On Taric, Alistar and Sona, GP10 seals are okey if you plan on playing deffensive (maxing heals, allowin the AD to farm). If you want to play aggressive on these 3 too (which I, personally, would recommend) you should get Armor seals isntead.
Some "pro" supports even tend to switch their GP10 Quints for Armor/MS/HP quints.
Basicly, not taking gp10 runes is a high risk high reward action on every aggressive support.
This might help you: https://docs.google.com/presentation/pub?id=1kWovClhppZJ7VWr3OSYIF671MhShKY6wRJZoLOH3-OE&start=false&loop=false#slide=id.p14
Its a guide for supporting from spellsy, a 2k elo guy. It has a own rune seciton.