I had a nice big post typed up about why this is wrong. Then my computer crashed. Again. So, I'll summarize. All that follows assumes that you know the target will die in 15 seconds (or enrage and all your dots are about to vanish, or something).
Bio, 5xRuin is 600 potency and costs 501 MP. That's about 1.2 potency/MP. Not horrible, but not the best.
Best damage is Bio2, Bio, Miasma, 3xRuin at 700 potency (You can switch B2 and Miasma. If they don't run full duration the order doesn't matter). This costs 635 MP, though, and that only gives you about 1.1 potency/MP. More damage, less efficient (again, over 15 seconds only).
Most efficient was, iirc, Bio, Miasma, 4xRuin at 680 potency for 555 MP, or 1.23 potency/MP. I want to say that Miasma->Bio was second best efficiency at the same MP cost for 5 less potency.
So, plenty of combinations are simultaneously more potent and more efficient than Ruin spam. This should not be a surprise to anyone remotely familiar with Ruin.