I also really enjoy summoner in Frontlines. I have more instant cast abilities than blm, so I can run a lot more often and use Ruin II, Energy Drain, Fester if DOTS are up, and Bio. Plus, the pet keeps attacking even while I'm on the move. Plus, with the lack of sleep and Flare, I'm less of a target than black mages are.

The pet is the only thing that can get annoying. Garuda just loves to follow my target even if they run away. Even pressing heel, she'll come back and heel for a bit, but then fly away again. So, just be prepared to Swift/re-summon her often.