Regardless of OP's reason, they aren't wrong... Gemshine and Precious Brilliance serve the same function as Ruin/Astral Impulse/Fountain of Fire and Outburst/Astral Flare/Brand of Purgatory.

I have yet to run into a situation where you would chose to cast Ruin instead of a Gemshine when it's active with a Rite. Has anyone else? I haven't run any low level stuff on summoner so perhaps there is a reason for their choice in this earlier on?