Nah. There's a middleground of things worth your time, that you can discover fairly easily.
When you're getting 50 runes per enemy and you need 5,000 to level, run past em because you'll soon find enemies that net you 2000 runes per kill. If you find an enemy that gives good runes, then consider grinding killing it.
Bosses give decent runes, but I don't think they'll float ya (and I hate that git gud shit. I suck bad and only barely squeaked by a win by getting absurdly overleveled with an OP weapon).