Melee in warframe feels weaker lately, what are people using?

It isn't weaker, the meta moved while you were away. Three things changed. Incarnon adapters, from Duviri's circuit, turned a few old weapons into monsters. Melee arcanes, which need the arcane adapter from steel path, and Melee Influence in particular is the build now, electric status spreading to everything nearby. And Tennokai, the heavy-attack proc system. So: Dual Ichor, Hate or Ceramic Dagger with their incarnons, Innodem, Praedos, Nami Skyla Prime, all with Melee Influence and electric. Blood Rush, Weeping Wounds, Condition Overload, Primed Pressure Point, Organ Shatter, the usual. Stances matter much less than they used to. Your old build is probably just missing the arcane slot, that alone is the gap you're feeling.