Need help with late game(steel path, Eidolons, etc.)

I've been playing Warframe for a long time, but mostly only collecting weapons, and frame, never really tried any late game content. Searched some guide for steel path. Build a Saryn prime and a Gauss prime. Weapon using Acceltra or Felmin, melee using Orthos(I like polearms because you can attack while sprinting). With these 2 frame, I'm either not killing anything(Gauss) or cannot stop dying(Saryn). Do I have to have good Raven mods? What am I missing? Is pet important? I'm just using a drone for the Vacuum.