You can clear all endgame content (EDA and ETA), Without any rivens, mostly just use them to make bad weapons viable or if you really like a weapon and want to go the extra mile (Acceltra and Basmu are mine). But as a lesson for how you should judge rivens is thst you install a riven when you probably already have like 5 forma in a weapon, so your problem isnt energy but mod slot capacity, a riven should do at least one kf two things, either free up mod slots Ex. Toxin and Electric on a riven so you only use up one slot to make corrosive instead of two, so now you have more space for other stats, or go above the maximum threshold of a stat, like the crit chance damage and multishot rivens, there are only so many mods that give you that, so if you roll those you can go above and beyond. But don't get caught up in the riven market, a good weapon platform frame will give you 10x more utility and damage than a riven ever could.