Summoner is possibly one of the most synergystic casters in this game, don't look at its class name, it only represents what the devs thought might be appropriate at the time. With nature pets and core dweller it is certainly not the worst full summoner, but with fire spells, plague, briar ward and heart of oak it is also one of the best casters in the game. Some people reported here that there are no mobs with high fire absorbtion in the game, so plague with fire spells should carry you through all difficulties. I'm only concerned about flame surge, at the times of main game and IT it was severely underperforming and I haven't tried it in Ragnarok to have an opinion. It might be better to go with tried and tested volcanic orb and eruption. Regardless of what you do, better try to incorporate eruption there, its one of the best aoe damage spells in the game for 12 points. And you won't be short on skill points in 70's.
/titancalc-anniversary-edition/TitanCalc44c344c344c3.html?mastery=Summoner&master1=4&master2=1&sa=30&m1=32-0-0-12-0-0-8-1-0-8-1-0-1-0-6-0-0-8-10-8-0&m2=32-12-0-8-12-0-12-1-16-0-1-5-0-1-0-1-0-12-12-5-12-0 Here is a plan for you
Core dweller is also an always get it crowd control option for earth casters.
~ Edit by efko ~ Links related with kirmiziperfect are unlinked. I left path just in case, but do not follow kirmiziperfect links since we are not checking if that site is used by someone else for other purposes, so it might contain malwares or something..